It started at one thirty on a cold Tuesday morning in January when Martin Turner, street performer and, in his own words, apprentice gigolo, tripped over a body in front of the West Portico of St Paul’s at Covent Garden. Martin, who was none too sober himself, at first thought the body was that of one of the many celebrants who had chosen the Piazza as a convenient outdoor toilet and dormitory. Being a seasoned Londoner, Martin gave the body the ‘London once-over’ – a quick glance to determine whether this was a drunk, a crazy or a human being in distress. The fact that it was entirely possible for someone to be all three simultaneously is why good-Samaritanism in London is considered an extreme sport – like base-jumping or crocodile-wrestling. Martin, noting the good-quality coat and shoes, had just pegged the body as a drunk when he noticed that it was in fact missing its head.

As Martin noted to the detectives conducting his interview, it was a good thing he’d been inebriated because otherwise he would have wasted time screaming and running about – especially once he realised he was standing in a pool of blood. Instead, with the slow, methodical patience of the drunk and terrified, Martin Turner dialled 999 and asked for the police.

The police emergency centre alerted the nearest Incident Response Vehicle and the first officers arrived on the scene six minutes later. One officer stayed with a suddenly sober Martin while his partner confirmed that there was a body and that, everything else being equal, it probably wasn’t a case of accidental death. They found the head six metres away where it had rolled behind one of the neoclassical columns that fronted the church’s portico. The responding officers reported back to control, who alerted the area Murder Investigation Team whose duty officer, the most junior detective constable on the team, arrived half an hour later: he took one look at Mr Headless and woke his governor. With that, the whole pomp and majesty that is a Metropolitan Police murder investigation descended on the twenty-five metres of open cobbles between the church portico and the market building. The pathologist arrived to certify death, make a preliminary assessment of the cause and cart the body away for its post-mortem. (There was a short delay while they found a big enough evidence bag for the head.) The forensic teams turned up mob-handed and, to prove that they were the important ones, demanded that the secure perimeter be extended to include the whole west end of the Piazza. To do this they needed more uniforms at the scene, so the DCI who was Senior Investigating Officer called up Charing Cross nick and asked if they had any to spare. The shift commander, upon hearing the magic word ‘overtime’, marched into the section house and volunteered everyone out of their nice warm beds. Thus the secure perimeter was expanded, searches were made, junior detectives sent off on mysterious errands and finally, at just after five o’clock, it all ground to a halt. The body was gone, the detectives had left and the forensic people unanimously agreed there was nothing more that could be done until dawn – which was three hours away. Until then, they just needed a couple of mugs to guard the crime scene until shift change.

Which is how I came to be standing around Covent Garden in a freezing wind at six o’clock in the morning, and why it was me that met the ghost.

Sometimes I wonder whether, if I’d been the one that went for coffee and not Lesley May, my life would have been much less interesting and certainly much less dangerous. Could it have been anyone, or was it destiny? When I’m considering this I find it helpful to quote the wisdom of my father, who once told me, ‘Who knows why the fuck anything happens?’

Covent Garden is a large piazza in the centre of London, with the Royal Opera House at the east end, a covered market in the centre and St Paul’s Church at the west end. It was once London’s principal fruit and veg market but that got shifted south of the river ten years before I was born. It had a long and varied history, mostly involving crime, prostitution and the theatre, but now it’s a tourist market. St Paul’s church is known as the Actors’ Church, to differentiate it from the Cathedral, and was first built by Inigo Jones in 1638. I know all this because there’s nothing like standing around in a freezing wind to make you look for distractions, and there was a large and remarkably detailed information plaque attached to the side of the church. Did you know, for instance, that the first recorded victim of the 1665 plague outbreak, the one that ends with London burning down, is buried in its graveyard? I did, after ten minutes spent sheltering from the wind.

The Murder Investigation Team had closed off the west of the Piazza by stringing tape across the entrances to King Street and Henrietta Street, and along the frontage of the covered market. I was guarding the church end, where I could shelter in the portico and WPC Lesley May, my fellow probationer, guarded the Piazza side, where she could shelter in the market.

Lesley was short, blonde and impossibly perky, even when wearing a stab vest. We’d gone through basic training at Hendon together before being transferred to Westminster for our probation. We maintained a strictly professional relationship, despite my deep-seated yearning to climb into her uniform trousers.

Because we were both probationary constables, an experienced PC had been left to supervise us – a responsibility he diligently pursued from an all-night café on St Martin’s Court.

My phone rang. It took me a while to dig it out from among the stab vest, utility belt, baton, handcuffs, digital police radio and cumbersome but mercifully waterproof reflective jacket. When I finally managed to answer, it was Lesley.

‘I’m going for a coffee,’ she said. ‘Want one?’

I looked over at the covered market and saw her wave.

‘You’re a life-saver,’ I said, and watched as she darted off towards James Street.

She hadn’t been gone more than a minute when I saw a figure by the portico. A short man in a suit tucked into the shadows behind the nearest column.

I gave the prescribed Metropolitan police ‘first greeting’.

‘Oi!’ I said. ‘What do you think you’re doing?’

The figure turned and I saw a flash of a pale, startled-looking face. The man was wearing a shabby, old-fashioned suit complete with waistcoat, fob watch and battered top hat. I thought he might be one of the street performers licensed to perform in the piazza, but it seemed a tad early in the morning for that.

‘Over here,’ he said, and beckoned.

I made sure I knew where my extendable baton was and headed over. Policemen are supposed to loom over members of the public, even helpful ones. That’s why we wear big boots and pointy helmets, but when I got closer I found the man was tiny, five foot nothing in his shoes. I fought an urge to squat down to get our faces level.

‘I saw the whole thing, squire,’ said the man. ‘Terrible thing, it was.’

They drum it into you at Hendon: before you do anything else, get a name and an address. I produced my notebook and pen. ‘Can I ask your name, sir?’

‘’Course you can, squire. My name’s Nicholas Wall-penny, but don’t ask me how to spell it because I never really got my letters.’

‘Are you a street performer?’ I asked.

‘You might say that,’ said Nicholas. ‘Certainly my performances have hitherto been confined to the street. Though on a cold night like this I wouldn’t be averse to bringing some interiority to my proceedings. If you catch my meaning, squire.’

There was a badge pinned to his lapel: a pewter skeleton caught mid-caper. It seemed a bit goth for a short cockney geezer, but then London is the pick ’n’ mix cultural capital of the world. I wrote down Street performer.

‘Now sir,’ I said, ‘if you could just tell me what it was you saw.’

‘I saw plenty, squire.’

‘But you were here earlier this morning?’ My instructors were also clear about not cueing your witnesses. Information is only supposed to flow in one direction.

‘I’m here morning, noon and night,’ said Nicholas, who obviously hadn’t gone to the same lectures I had.

‘If you’ve witnessed something,’ I said, ‘perhaps you’d better come and give a statement.’

‘That would be a bit of problem,’ said Nicholas, ‘seeing as I’m dead.’

I thought I hadn’t heard him correctly. ‘If you’re worried about your safety …’

‘I ain’t worried about anything any more, squire,’ said Nicholas. ‘On account of having been dead these last hundred and twenty years.’

‘If you’re dead,’ I said before I could stop myself, ‘how come we’re talking?’

‘You must have a touch of the sight,’ said Nicholas. ‘Some of the old Palladino.’ He looked at me closely. ‘Touch of that from your father, maybe? Dockman, was he, sailor, some such thing, he gave you that good curly hair and them lips?’

‘Can you prove you’re dead?’ I asked.

‘Whatever you say, squire,’ said Nicholas, and stepped forward into the light.

He was transparent, the way holograms in films are transparent. Three-dimensional, definitely really there and fucking transparent. I could see right through him to the white tent the forensic team had set up to protect the area around the body.

Right, I thought, just because you’ve gone mad doesn’t mean you should stop acting like a policeman.

‘Can you tell me what you saw?’ I asked.

‘I saw the first gent, him that was murdered, walking down from James Street. Fine, high-stepping man with a military bearing, very gaily dressed in the modern fashion. What I would have considered a prime plant in my corporeal days.’ Nicholas paused to spit. Nothing reached the ground. ‘Then the second gent, him what did the murdering, he comes strolling the other way up from Henrietta Street. Not so nicely turned out, wearing them blue workman’s trousers and an oilskin like a fisherman. They passed each other just there.’ Nicholas pointed to a spot ten metres short of the church portico. ‘I reckon they know each other, ’cause they both nod but they don’t stop for a chat or nothing, which is understandable, it not being a night for loitering.’

‘So they passed each other?’ I asked, as much for the chance to catch up with my note-taking as to clarify the point. ‘And you thought they knew each other?’

‘As acquaintances,’ said Nicholas. ‘I wouldn’t say they were bosom friends, especially with what transpired next.’

I asked him what transpired next.

‘Well the second, murdering gent, he puts on a cap and a red jacket and he brings out his stick and as quietly and swiftly as a snoozer in a lodging house he comes up behind the first gent and knocks his head clean off.’

‘You’re having me on,’ I said.

‘No I’m never,’ said Nicholas, and crossed himself. ‘I swear on my own death, and that’s as solemn a swear as a poor shade can give. It was a terrible sight. Off came his head and up went the blood.’

‘What did the killer do?’

‘Well, having done his business he was off, went down New Row like a lurcher on the commons,’ said Nicholas.

I was thinking that New Row took you down to Charing Cross Road, an ideal place to catch a taxi or a minicab or even a night bus if the timing was right. The killer could have cleared central London in less than fifteen minutes.

‘That wasn’t the worst of it,’ said Nicholas, obviously unwilling to let his audience get distracted. ‘There was something uncanny about the killing gent.’

‘Uncanny?’ I asked. ‘You’re a ghost.’

‘Spirit I may be,’ said Nicholas. ‘But that just means I know uncanny when I see it.’

‘And what did you see?’

‘The killing gentleman didn’t just change his hat and coat, he changed his face,’ said Nicholas. ‘Now tell me that ain’t uncanny.’

Someone called my name. Lesley was back with the coffees.

Nicholas vanished while I wasn’t looking.

I stood staring like an idiot for a moment until Lesley called again.

‘Do you want this coffee or not?’ I crossed the cobbles to where the angel Lesley was waiting with a polystyrene cup. ‘Anything happen while I was away?’ she asked. I sipped my coffee. The words – I just talked to a ghost who saw the whole thing – utterly failed to leave my lips.

The next day I woke up at eleven – much earlier than I wanted to. Lesley and I had been relieved at eight, and we’d trudged back to the section house and gone straight to bed. Separate beds, unfortunately.

The principal advantages of living in your station’s section house is that it is cheap, close to work and it’s not your parents’ flat. The disadvantages are that you’re sharing your accommodation with people too weakly socialised to live with normal human beings, and who habitually wear heavy boots. The weak socialisation makes opening the fridge an exciting adventure in microbiology, and the boots mean that every shift change sounds like an avalanche.

I lay in my narrow little institutional bed staring at the poster of Estelle that I’d affixed to the wall opposite. I don’t care what they say: you’re never too old to wake up to the sight of a beautiful woman.

I stayed in bed for ten minutes, hoping that my memory of talking to a ghost might fade like a dream, but it didn’t, so I got up and had a shower. It was an important day that day, and I had to be sharp.

The Metropolitan Police Service is still, despite what people think, a working-class organisation and as such rejects totally the notion of an officer class. That is why every newly minted constable, regardless of their educational background, has to spend a two-year probationary period as an ordinary plod on the streets. This is because nothing builds character like being abused, spat at and vomited on by members of the public.

Towards the end of your probation you start applying for positions in the various branches, directorates and operational command units that make up the force. Most probationers will continue on as full uniformed constables in one of the borough commands, and the Met hierarchy likes to stress that deciding to remain a uniformed constable doing vital work on the streets of London is a positive choice in and of itself. Somebody has to be abused, spat at and vomited on, and I for one applaud the brave men and women who are willing to step up and serve in that role.

This had been the noble calling of my shift commander, Inspector Francis Neblett. He had joined the Met back in the time of the dinosaurs, had risen rapidly to the rank of Inspector and then spent the next thirty years quite happily in the same position. He was a stolid man with lank brown hair and a face that looked as if it had been struck with the flat end of a shovel. Neblett was old-fashioned enough to wear a uniform tunic over his regulation white shirt, even when out patrolling with ‘his lads’.

I was scheduled to have an interview with him today, at which we would ‘discuss’ my future career prospects. Theoretically this was part of an integrated career development process that would lead to positive outcomes with regards to both the police service and me. After this discussion a final decision as to my future disposition would be made – I strongly suspected that what I wanted to do wouldn’t enter into it.

Lesley, looking unreasonably fresh, met me in the squalid kitchenette shared by all the residents on my floor. There was paracetamol in one of the cupboards; one thing you can always be certain of in a police section house is that there will always be paracetamol. I took a couple and gulped water from the tap.

‘Mr Headless has a name,’ she said, while I made coffee. ‘William Skirmish, media type, lives up in Highgate.’

‘Are they saying anything else?’

‘Just the usual,’ said Lesley. ‘Senseless killing, blah, blah. Inner-city violence, what is London coming to, blah.’

‘Blah,’ I said.

‘What are you doing up before noon?’ she asked.

‘Got my career progression meeting with Neblett at twelve.’

‘Good luck with that,’ she said.

I knew it was all going pear-shaped when Inspector Neblett called me by my first name.

‘Tell me, Peter,’ he said. ‘Where do you see your career going?’

I shifted in my chair.

‘Well, sir,’ I said, ‘I was thinking of CID.’

‘You want to be a detective?’ Neblett was, of course, a career ‘uniform’, and thus regarded plain-clothes police officers in much the same way as civilians regard tax inspectors. You might, if pressed, concede that they were a necessary evil but you wouldn’t actually let your daughter marry one.

‘Yes, sir.’

‘Why limit yourself to CID?’ he asked. ‘Why not one of the specialist units?’

Because you don’t, not when you’re still on probation, say that you want to be in the Sweeney or a Murder Investigation Team and swan around in a big motor while wearing handmade shoes.

‘I thought I’d start at the beginning and work my way up, sir,’ I said.

‘That’s a very sensible attitude,’ said Neblett.

I suddenly had a horrible thought. What if they were thinking of sending me to Trident? That was the Operational Command Unit charged with tackling gun crime within the black community. Trident was always on the lookout for black officers to do hideously dangerous undercover work, and being mixed race meant that I qualified. It’s not that I don’t think they do a worthwhile job, it’s just that I didn’t think I’d be very good at it. It’s important for a man to know his limitations, and my limitations started at moving to Peckham and hanging around with yardies, postcode wannabes and those weird, skinny white kids who don’t get the irony in Eminem.

‘I don’t like rap music, sir,’ I said.

Neblett nodded slowly. ‘That’s useful to know,’ he said, and I resolved to keep a tighter grip on my mouth.

‘Peter,’ he said, ‘over the last two years I’ve formed a very positive opinion of your intelligence and your capacity for hard work.’

‘Thank you, sir.’

‘And then there is your science background.’

I have three C-grade A levels in Maths, Physics and Chemistry. This is only considered a science background outside of the scientific community. It certainly wasn’t enough to get me the university place I wanted.

‘You’re very useful at getting your thoughts down on paper,’ said Neblett.

I felt a cold lump of disappointment in my stomach. I knew exactly what horrifying assignment the Metropolitan Police had planned for me.

‘We want you to consider the Case Progression Unit,’ said Neblett.

The theory behind the Case Progression Unit is very sound. Police officers, so the established wisdom has it, are drowning in paperwork, suspects have to be logged in, the chain of evidence must never be broken and the politicians and PACE, the Police And Criminal Evidence Act, must be followed to the letter. The role of the Case Progression Unit is to do the paperwork for the hard-pressed constable so he or she can get back out on the street to be abused, spat at and vomited on. Thus will there be a bobby on the beat, and thus shall crime be defeated and the good Daily Mail-reading citizens of our fair nation shall live in peace.

The truth is that the paperwork is not that onerous – any half-competent temp would dispose of it in less than an hour and still have time to do his nails. The problem is that police work is all about ‘face’ and ‘presence’ and remembering what a suspect said one day so you can catch them in a lie on the next. It’s about going towards the scream, staying calm and being the one that opens a suspect package. It’s not that you can’t do both, it’s just that it’s not exactly common. What Neblett was saying to me was that I wasn’t a real copper – not a thief taker – but I might play a valuable role freeing up real coppers. I could tell with a sick certainty that those very words ‘valuable role’ were rushing towards the conversation.

‘I was hoping for something a bit more proactive, sir,’ I said.

‘This would be proactive,’ said Neblett. ‘You’d be performing a valuable role.’

Police officers, as a rule, don’t need an excuse to go to the pub, but one of the many non-excuses they have is the traditional end-of-probation booze-up when members of the shift get the brand new full constables completely hammered. To that end, Lesley and me were dragged across the Strand to the Roosevelt Toad and plied with alcohol until we were horizontal. That was the theory, anyway.

‘How did it go?’ Lesley asked over the roar of the pub.

‘Badly,’ I shouted back. ‘Case Progression Unit.’

Lesley pulled a face.

‘What about you?’

‘I don’t want to tell you,’ she said. ‘It’ll piss you off.’

‘Hit me,’ I said. ‘I can take it.’

‘I’ve been temporarily assigned to the murder team,’ she said.

I’d never heard of that happening before. ‘As a detective?’

‘As a uniformed constable in plain clothes,’ she said. ‘It’s a big case and they need bodies.’

She was right. It did piss me off.

The evening went sour after that. I stuck it out for a couple of hours but I hate self-pity, especially mine, so I went out and did the next best thing to sticking my head in a bucket of cold water.

Unfortunately it had stopped raining while we were in the pub, so I settled for letting the freezing air sober me up.

Lesley caught up with me twenty minutes later.

‘Put your bloody coat on,’ she said. ‘You’ll catch your death.’

‘Is it cold?’ I asked.

‘I knew you’d be upset,’ she said.

I put my coat on. ‘Have you told the tribe yet?’ I asked. In addition to her mum, her dad and nan, Lesley had five older sisters, all still resident within a hundred metres of the family home in Brightlingsea. I’d met them once or twice when they’d descended upon London en masse for a shopping expedition. They were loud to the point of constituting a one-family breach of the peace, and would have merited a police escort if they hadn’t already had one, i.e. Lesley and me.

‘This afternoon,’ she said. ‘They were well-pleased. Even Tanya, and she doesn’t even know what it means. Have you told yours yet?’

‘Tell them what?’ I asked. ‘That I work in an office?’

‘Nothing wrong with working in an office.’

‘I just want to be a copper,’ I said.

‘I know,’ said Lesley. ‘But why?’

‘Because I want to help the community,’ I said. ‘Catch bad guys.’

‘Not the shiny buttons, then?’ she asked. ‘Or the chance to slap the cuffs on and say, “You’re nicked, my son”?’

‘Maintain the Queen’s peace,’ I said. ‘Bring order out of chaos.’

She shook her head sadly. ‘What makes you think there’s any order?’ she said. ‘And you’ve been out on patrol on a Saturday night. Does that look like the Queen’s peace?’

I went to lean nonchalantly against a lamp post but it went wrong and I staggered around a bit. Lesley found this much funnier than I thought it really deserved. She sat down on the step of Waterstone’s bookshop to catch her breath.

‘Okay,’ I said. ‘Why are you in the job?’

‘Because I’m really good at it,’ said Lesley.

‘You’re not that good a copper,’ I said.

‘Yes I am,’ she said. ‘Let’s be honest, I’m bloody amazing as a copper.’

‘And what am I?’

‘Too easily distracted.’

‘I am not.’

‘New Year’s Eve, Trafalgar Square, big crowd, bunch of total wankers pissing in the fountain – remember that?’ asked Lesley. ‘Wheels come off, wankers get stroppy and what were you doing?’

‘I was only gone for a couple of seconds,’ I said.

‘You were checking what was written on the lion’s bum,’ said Lesley. ‘I was wrestling a couple of drunken chavs and you were doing historical research.’

‘Do you want to know what was on the lion’s bum?’ I asked.

‘No,’ said Lesley, ‘I don’t want to know what was written on the lion’s bum, or how siphoning works or why one side of Floral Street is a hundred years older than the other side.’

‘You don’t think any of that’s interesting?’

‘Not when I’m wrestling chavs, catching car thieves or attending a fatal accident,’ said Lesley. ‘I like you, I think you’re a good man, but it’s like you don’t see the world the way a copper needs to see the world – it’s like you’re seeing stuff that isn’t there.’

‘Like what?’

‘I don’t know,’ said Lesley. ‘I can’t see stuff that isn’t there.’

‘Seeing stuff that isn’t there can be a useful skill for a copper,’ I said.

Lesley snorted.

‘It’s true,’ I said. ‘Last night while you were distracted by your caffeine dependency I met an eyewitness who wasn’t there.’

‘Wasn’t there,’ said Lesley.

‘How can you have an eyewitness who wasn’t there, I hear you ask?’

‘I’m asking,’ said Lesley.

‘When your eyewitness is a ghost,’ I said.

Lesley stared at me for a moment. ‘I would have gone with the CCTV camera controller myself,’ she said.

‘What?’

‘Guy watching the murder on CCTV,’ said Lesley. ‘He’d be a witness who wasn’t there. But I like the ghost thing.’

‘I interviewed a ghost,’ I said.

‘Bollocks,’ said Lesley.

So I told her about Nicholas Wallpenny and the murdering gent who turned back, changed his clothes and then knocked poor– ‘What was the victim’s name again?’ I asked.

‘William Skirmish,’ said Lesley. ‘It was on the news.’

‘Knocked poor William Skirmish’s head clean off his shoulders.’

‘That wasn’t on the news,’ said Lesley.

‘The murder team will want to keep that back,’ I said. ‘For witness verification.’

‘The witness in question being a ghost?’ asked Lesley.

‘Yes.’

Lesley got to her feet, swayed a bit and then got her eyes focused again. ‘Do you think he’s still there?’ she asked.

The cold air was beginning to sober me up at last. ‘Who?’

‘Your ghost,’ she said, ‘Nicholas Nickleby. Do you think he might still be at the crime scene?’

‘How should I know?’ I said. ‘I don’t even believe in ghosts.’

‘Let’s go and see if he’s there,’ she said. ‘If I see him too then it will be like corob … like crob … proof.’

‘Okay,’ I said.

We wandered arm in arm up King Street towards Covent Garden.

There was a great absence of Nicholas the ghost that night. We started at the church portico where I’d seen him and, because Lesley was a thoroughgoing copper even when pissed, did a methodical search around the perimeter.

‘Chips,’ said Lesley after our second circuit. ‘Or a kebab.’

‘Maybe he doesn’t come out when I’m with someone else,’ I said.

‘Maybe he does shift work,’ said Lesley.

‘Fuck it,’ I said. ‘Let’s have a kebab.’

‘You’ll be good at the Case Progression Unit,’ said Lesley. ‘And you’ll be …’

‘If you say “… making a valuable contribution” I will not be held responsible for my actions.’

‘I was going to say “making a difference”,’ she said. ‘You could always go to the states, I bet the FBI would have you.’

‘Why would the FBI have me?’ I asked.

‘They could use you as an Obama decoy,’ she said.

‘For that,’ I said, ‘you can pay for the kebabs.’

In the end we were too knackered to get kebabs, so we headed straight back to the section house where Lesley utterly failed to invite me to her room. I was at that stage of drunk where you lie on your bed in the dark and the room goes whirling around you, and you’re wondering about the nature of the universe and whether you can get to the sink before you throw up.

Tomorrow was my last day off, and unless I could prove that seeing things that weren’t there was a vital skill for the modern police officer, it was hello Case Progression Unit for me.

‘I’m sorry about last night,’ said Lesley.

Neither of us could face the horrors of the kitchenette that morning, so we found shelter in the station canteen. Despite the fact that the catering staff were a mixture of compact Polish women and skinny Somali men, a strange kind of institutional inertia meant that the food was classic English greasy spoon, the coffee was bad and the tea was hot, sweet and came in mugs. Lesley was having a full English breakfast; I was having a tea.

‘It’s all right,’ I said. ‘Your loss, not mine.’

‘Not that,’ said Lesley, and smacked me on the hand with the flat of her knife. ‘What I said about you being a copper.’

‘Don’t worry,’ I said. ‘I’ve taken your feedback on board, and having extensively workshopped it this morning I now feel that I can pursue my core career-development goals in a diligent, proactive but, above all, creative manner.’

‘What are you planning to do?’

‘I’m going to hack HOLMES to see if my ghost was right,’ I said.

*

Every police station in the country has at least one HOLMES suite. This is the Home Office Large Major Enquiry System, which allows computer-illiterate coppers to join the late twentieth century. Getting them to join the twenty-first century would be too much to ask for.

Everything related to a major investigation is kept on the system, allowing detectives to cross-reference data and avoid the kind of cock-up that made the hunt for the Yorkshire Ripper such an exemplary operation. The replacement to the old system was due to be called SHERLOCK, but nobody could find the words to make the acronym work so they called it HOLMES 2.

Theoretically you can access HOLMES 2 from a laptop, but the Metropolitan Police likes to keep its personnel tied to fixed terminals – which can’t be left in trains or sold to pawn shops. When a major investigation occurs, the terminals can be transferred from the suite to incident rooms elsewhere in the station. Lesley and I could have sneaked into the HOLMES suite and risked being caught, but I preferred to plug my laptop into a LAN socket in one of the empty incident rooms and work in safety and comfort.

I’d been sent on a HOLMES 2 familiarisation course three months earlier. At the time I’d been excited because I thought they might be preparing me for a role in major investigations, but now I realise they were grooming me for data entry work. It took me less than half an hour to find the Covent Garden investigation. People are often negligent about passwords, and Inspector Neblett had used his youngest daughter’s name and year of birth, which is just criminal. It also got me read-only access to the files we wanted.

The old system couldn’t handle big data files, but because HOLMES 2 was only ten years behind the state of the art, detectives could now attach evidence photographs, document scans and even CCTV footage directly to what’s called a ‘nominal record’ file. It’s like YouTube for cops.

The Murder Team assigned to the William Skirmish murder had wasted no time grabbing the CCTV footage and seeing if they could get a look at the murderer. It was a big fat file and I went straight for it.

According to the report, the camera was mounted on the corner of James Street, looking west. It was low-quality, low-light footage updated at one frame per second. But despite the poor light it clearly showed William Skirmish walking from under the camera towards Henrietta Street.

‘There’s our suspect,’ said Lesley, pointing.

The screen showed another figure – the best you could say was probably male, probably in jeans and a leather jacket – walk past William Skirmish and vanish below the screen. According to the notes, this figure was being designated WITNESS A.

A third figure appeared, going away from the camera. I hit pause.

‘Doesn’t look like the same guy,’ said Lesley.

Definitely not. This man was wearing what looked like a Smurf hat and what l recognised as an Edwardian smoking jacket – don’t ask me why I know what an Edwardian smoking jacket looks like: let’s just say it has something to do with Doctor Who and leave it at that. Nicholas had said it was red, but the CCTV image was in black and white. I clicked back a couple of frames and then forward again. The first figure, WITNESS A, dropped out of shot one, two frames before the man in the smurf hat stepped into view.

‘That’s two seconds to get changed,’ said Lesley. ‘That’s not humanly possible.’

I clicked forward. The man in the smurf hat produced his bat and stepped smartly up behind William Skirmish. The wind-up was between frames but the hit was clear. In the next frame Skirmish’s body was halfway to the ground and a little dark blob, which we decided must be the head, was just visible by the portico.

‘My God. He really did knock his head clean off,’ said Lesley.

Just as Nicholas had said he had.

‘Now that,’ I said, ‘is not humanly possible.’

‘You’ve seen a head come off before,’ said Lesley. ‘I was there, remember?’

‘That was a car accident,’ I said. ‘That’s two tons of metal, not a bat.’

‘Yeah,’ said Lesley, tapping the screen. ‘But there it is.’

‘There’s something wrong here.’

‘Apart from the horrible murder?’

I clicked back to where Smurf Hat entered the scene. ‘Can you see a bat?’

‘No,’ said Lesley. ‘Both his hands are visible. Maybe it’s on his back.’

I clicked forward. On the third frame the bat appeared in Smurf Hat’s hands as if by magic, but that could just have been an artefact of the one-second lag between frames. There was something else wrong with it too.

‘That’s much too big to be a baseball bat,’ I said.

The bat was at least two-thirds as long as the man who carried it. I clicked backwards and forwards a few times but I couldn’t work out where he was keeping it.

‘Maybe he likes to speak really softly,’ said Lesley.

‘Where do you even buy a bat that size?’

‘The Big Bat Shop?’ said Lesley. ‘Bats R Us?’

‘Let’s see if we can get a look at his face,’ I said.

‘Plus Size Bats,’ said Lesley.

I ignored her and clicked forward. The murder took less than three seconds, three frames: one the wind-up, two the blow and three the follow-through. The next frame caught Smurf Hat mid-turn, his face in three-quarter profile showing a jutting chin and a prominent hook nose. The frame after showed Smurf Hat walking back the way he’d come, slower than the approach, casual as far as I could tell from the stuttering image. The bat vanished two frames after the murder – again, I couldn’t see where it had gone.

I wondered if we could enhance the faces, and started looking for a graphic function I could use.

‘Idiot,’ said Lesley. ‘Murder Team will be all over that.’

She was right. Connected to the footage were links to enhanced pictures of William Skirmish, WITNESS A and the murdering gent in the smurf hat. Contrary to television, there’s an absolute limit to how good a closeup you can extrapolate from an old-fashioned bit of video tape. It doesn’t matter if it’s digital – if the information isn’t there, it isn’t there. Still, someone at the tech lab had done their best, and despite all the faces being blurry it was at least obvious that all three were different people.

‘He’s wearing a mask,’ I said.

‘Now you’re getting desperate,’ said Lesley.

‘Look at that chin and that nose,’ I said. ‘Nobody has a face like that.’

Lesley pointed to a notation attached to the image. ‘Looks like the Murder Team agree with you.’ There was a list of ‘actions’ associated with the evidence file, one of which was to check local costumiers, theatres and fancy-dress shops for masks. It had a very low priority.

‘Aha!’ I said. ‘So it might be the same person.’

‘Who can change their clothes in less than two seconds?’ asked Lesley. ‘Do me a favour.’

All the evidence files are linked, so I checked to see whether the Murder Team had managed to track WITNESS A as he left the crime scene. They hadn’t and, according to the action list, finding him had become a priority. I predicted a press conference and an appeal for witnesses. Police are particularly interested in talking to . . . would be the relevant phrase there.

Smurf Hat had been tracked all the way down New Row, exactly the route Nicholas had said he’d taken, but vanished off the surveillance grid in St Martin’s Lane. According to the ‘action’ list, half the Murder Team were currently scouring the surrounding streets for potential witnesses and clues.

‘No,’ said Lesley, reading my mind.

‘Nicholas …’

‘Nicholas the ghost,’ said Lesley.

‘Nicholas the corporeally challenged,’ I said, ‘was right about the murderer’s approach, the method of attack and cause of death. He was also right about the getaway route, and we don’t have a timeline where WITNESS A is visible at the same time as Smurf Hat.’

‘Smurf Hat?’

‘The murder suspect,’ I said. ‘I need to take this to the Murder Team.’

‘What are you going to say to the SIO?’ asked Lesley. ‘I met a ghost and he said that WITNESS A put on a mask and did it?’

‘No, I’m going to say that I was approached by a potential witness who, despite leaving the scene before I could get his name and address, generated potentially interesting leads that may further the successful outcome of the investigation.’

It made Lesley pause at least. ‘And you think that’ll get you out of the Case Progression Unit?’

‘It’s got to be worth a try,’ I said.

‘It’s not enough,’ said Lesley. ‘One: they’re already generating leads over WITNESS A, including the possibility that he was wearing a mask. Two: you could have got all that information from the video.’

‘They won’t know I had access to the video.’

‘Peter,’ said Lesley. ‘It shows someone’s head being knocked off. It’s going to be all over the internet by the end of the day, and that’s if it’s not on the ten o’clock news.’

‘Then I’ll generate more leads,’ I said.

‘You’re going to go looking for your ghost?’

‘Want to come?’

‘No,’ said Lesley. ‘Because tomorrow is the most important day of the rest of my career, and I am going to bed early with a cocoa and a copy of Blackstone’s Police Investigator’s Workbook.’

‘Just as well,’ I said. ‘I think you scared him away last night, anyway.’

Equipment for ghost hunters: thermal underwear, very important; warm coat; thermos flask; patience; ghost.

It did occur to me quite early on that this was possibly the most absurd thing I’d ever done. Around ten I took up my first position, sitting at an outdoor table of a café, and waited for the crowds to thin out. Once the café closed I sauntered over to the church portico and waited.

It was another freezing night, which meant that the drunks leaving the pubs were too cold to assault each other. At one point a hen party went past, a dozen women in oversized pink t-shirts, bunny ears and high heels. Their pale legs were blotchy with cold. One of them spotted me.

‘You’d better go home,’ she called. ‘He’s not coming.’

Her mates shrieked with laughter. I heard one of them complaining that ‘all the good-looking ones are gay’.

Which was what I was thinking when I saw the man watching me from the across the Piazza. What with the proliferation of gay pubs, clubs and chat rooms, it is no longer necessary for the single man about town to frequent public toilets and graveyards on freezing nights to meet the man of their immediate needs. Still, some people like to risk frostbite on their nether regions – don’t ask me why.

He was about one-eighty in height – that’s six foot in old money – and dressed in a beautifully tailored suit that emphasised the width of his shoulders and a trim waist. I thought early forties with long, finely boned features and brown hair cut into an old-fashioned side parting. It was hard to tell in the sodium light but I thought his eyes were grey. He carried a silver-topped cane and I knew without looking that his shoes were handmade. All he needed was a slightly ethnic younger boyfriend and I’d have had to call the cliché police.

When he strolled over to talk to me I thought he might be looking for that slightly ethnic boyfriend after all.

‘Hello,’ he said. He had a proper RP accent, like an English villain in a Hollywood movie. ‘What are you up to?’

I thought I’d try the truth. ‘I’m ghost-hunting,’ I said.

‘Interesting,’ he said. ‘Any particular ghost?’

‘Nicholas Wallpenny,’ I said.

‘What’s your name and address?’ he asked.

No Londoner ever answers that question unchallenged. ‘I beg your pardon?’

He reached into his jacket and pulled out his wallet. ‘Detective Chief Inspector Thomas Nightingale,’ he said, and showed me his warrant card.

‘Constable Peter Grant,’ I said.

‘Out of Charing Cross nick?’

‘Yes sir.’

He gave me a strange smile.

‘Carry on, Constable,’ he said, and went strolling back up James Street.

So there I was, having just told a senior Detective Chief Inspector that I was hunting ghosts, which, if he believed me, meant he thought I was bonkers, or if he didn’t believe me meant he thought I was cottaging and looking to perpetrate an obscene act contrary to public order.

And the ghost that I was looking for had failed to make an appearance.

Have you ever run away from home? I have, on two occasions. The first time, when I was nine, I only got as far as Argos on Camden High Street and the second time, aged fourteen, I made it all the way to Euston Station and was actually standing in front of the departure boards when I stopped. On both occasions I wasn’t rescued or found or brought back; indeed, when I returned home I don’t think my mum noticed I’d gone. I know my dad didn’t.

Both adventures ended the same way – with the realisation that in the end, no matter what, I was going to have to go home. For my nine-year-old self it was the knowledge that the Argos store represented the outer limit of my understanding of the world. Beyond that point was a tube station and a big building with statues of cats and, further on, more roads and bus journeys that led to downstairs clubs that were sad and empty and smelled of beer.

My fourteen-year-old self was more rational. I didn’t know anyone in these cities on the departure boards, and I doubted they would be any more welcoming than London. I probably didn’t even have enough money to get me further than Potters Bar, and even if I did stow away for free, what was I going to eat? Realistically I had three meals’ worth of cash on me, and then it would be back home to Mum and Dad. Anything I did short of getting back on the bus and going home was merely postponing the inevitable moment of my return.

I had that same realisation in Covent Garden at three o’clock in the morning. That same collapse of potential futures down to a singularity, a future that I couldn’t escape. I wasn’t going to drive a fancy motor and say ‘you’re nicked’. I was going to work in the Case Progression Unit and make a ‘valuable contribution’.

I stood up and started walking back to the nick.

In the distance I thought I could hear someone laughing at me.