I’d got the tube all the way to Swiss Cottage, and was a quarter of the way up Fitzjohn’s Avenue when I started to question what I was doing. It wasn’t just that I’d abandoned my motor for public transport, it was also that I was walking up one of the steepest hills in London when I could have taken the train to Hampstead and walked down the hill instead. It was still bright, and the afternoon sunlight cut through the gaps between the trees that lined the avenue. The flowers in my hand were roses, a purple variety that were so dark as to be almost black. I wondered who they might be for.

It was warm enough that I unclipped my tie and stuffed it into my jacket pocket. I didn’t want to arrive sweaty, so I took my time and ambled along in the shade of the plane trees planted along the pavement. It was the kind of day where a tune gets stuck in your head and you can’t help singing it out loud; in this case it was a blast from my past, ‘Digging Your Scene’ by the Blow Monkeys. Given that it was released when I was still in nappies, it was a wonder I knew all the words. I’d sung, ‘I’d just like to be myself again’ in the third chorus when I reached my destination. The house was a tall gothic confection with a mock tower at each corner and sash windows painted white. Marble-clad steps led up to an imposing front door but I ignored them and made my way to the side gate – I knew where I was going. I checked my jacket was straight and rubbed the toes of my shoes on the back of my calves; satisfied, I pushed open the gate and stepped through.

Honeysuckle had been planted along the side wall of the house, making a sweet-scented corridor that opened up into a wide, sunny garden. A neatly mown lawn was bordered by formal beds planted with surfinia petunias, marigold and tulips. Two huge terracotta pots bursting with spring flowers guarded the steps down to a sunken patio at the centre of which the afternoon sunlight pooled around a fountain. Even I could see that this wasn’t some piece picked up in a garden store or hypermarket. It was a delicate marble birdbath with a central statue of a nude carrying water; Italian Renaissance, maybe – I didn’t have enough art history to know. It was antique and battered, the marble chipped in places, and the nymph had a discoloured streak running from her shoulder to her groin made by the water trickling out of her gourd.

The water smelled sweet and enticing, just the thing after my long, slow walk up the hill. A handsome middle-aged woman was waiting for me by the fountain. She was dressed in a yellow cotton sundress, straw hat and open-toed sandals. As I drew closer I saw she had her mother’s eyes, black and slanted like a cat’s, but that she was lighter than Beverley with a nice, straight media-friendly nose.

There was once a gallows, close to where Marble Arch now stands, where they used to hang the criminals of old London town. The gallows was named after the village, whose inhabitants profited so greatly from the grisly spectacles that they built viewing stands to bring in the punters, which was named after the river that ran through it. The river was named the Tyburn. They hanged poor Elizabeth Barton there and Gentleman Jack, for all that he’d escaped four times before, and the Reverend James Hackman for the murder of pretty Martha Ray. I knew all this because after Beverley’d dropped her sister’s name into the conversation as the one who knows people who matter, I made a point of finding out.

‘I thought it was time you and I had a little chat,’ said Tyburn.

I offered her the flowers, which she took with a delighted laugh. She pulled my head down and kissed me on the cheek. She smelled of cigars and new car seats, horses and furniture polish, Stilton, Belgian chocolate and, behind it all, the hemp and the crowd and the last drop into oblivion.

I’d traced the sources, as well as I could anyway, of all the lost rivers of London. Some, like the Beverley Brook, the Lea or the Fleet were easy to find, but the location of the Tyburn, the legendary Shepherd’s Well, had got lost in the mad Victorian steam-powered expansion of London in the latter half of the nineteenth century. This fountain was obviously at the source, but the fountain itself, I suspected, had been looted by an enterprising official in the last days of the Empire.

I was thirsty – I would have liked a drink.

‘What would you like to talk about?’ I asked.

‘For a start,’ said Tyburn, ‘I’d like to know what your intentions are with regards to my sister.’

‘My intentions?’ I asked. My mouth was very dry. ‘My intentions are purely honourable.’

‘Really?’ she said, and crouched down to retrieve a vase from behind the fountain. ‘Is that why you took her to see the pikeys?’

Pikey is not a word a well brought-up young policeman is supposed to use. ‘That was just a preliminary, exploratory investigation,’ I said. ‘And Oxley and Isis are not pikeys.’

Tyburn drew the back of her hand down the back of the marble water carrier, and the trickle from the gourd thickened into a strong stream from which she filled the vase. ‘Still,’ she said as she unwrapped the roses, ‘not the sort of people one wants one’s sister associating with.’

‘We don’t get to choose our family,’ I said cheerfully. ‘Thank God we can choose our friends.’

Tyburn gave me a sharp look and started arranging the roses. The vase was unremarkable, fat-bottomed like a volumetric flask and made from green lacquered fibreglass, the sort of thing you can pick up for fifty pence at a car boot sale. ‘I’ve got nothing against the Old Man or his people, but this is the twenty-first century and this is my town, and I haven’t busted a gut for thirty years so that some “gentleman of the road” can move back in and take what’s mine.’

‘What do you think is yours?’ I asked.

She ignored me and, having arranged the last of the roses, placed the vase on the patio wall close by. When I’d bought them the roses had been the last of the stock and were beginning to wilt on the stand. Once Tyburn placed them in the vase they perked up, becoming full, rich and even darker.

‘Peter,’ she said, ‘you’ve seen the way the Folly is organised, or rather not organised. You know that it has no official standing in Government, and its relationship with the Metropolitan Police is entirely a matter of custom and practice and, God help me, tradition. It’s all held together with spit and sealing wax and the old boy network. It’s a typical British mash-up, and the one time it was asked to step up it failed horribly. I have access to files you don’t even know exist, Peter, about a place in Germany called Ettersburg – you might want to ask your mentor about that.’

‘Technically he’s my Master,’ I said. ‘I swore a guild oath as his apprentice.’ My tongue felt thick and dry, as if I’d just spent the night sleeping with my mouth open.

‘I rest my case,’ she said. ‘I know it’s against the national character but don’t you just wish we were a little bit more organised about these things, just a tad more grown-up? Would it kill us to have an official branch of government that handled the supernatural?’

‘A Ministry of Magic?’ I asked.

‘Ha-bloody-ha,’ said Tyburn.

I wanted to know why she hadn’t offered me a cup of tea. I’d brought her flowers, and figured the least I could expect in return would be a nice cup of tea or a beer, or even a drink of water. I cleared my throat and it came out a bit wheezy. I glanced at the fountain and the water streaming into the basin.

‘Do you like it?’ she asked. ‘The basin is a rather crude seventeenth-century knock-off of an Italian design, but the central figure was excavated when they were building Swiss Cottage station.’ She rested her hand on the statue’s face. ‘The marble’s from Belgium, but the archaeologists assure me that it was carved locally.’

I was having trouble working out why I didn’t want to drink the water. I’ve drunk water before, when beer, or coffee or Diet Coke weren’t available. I’ve drunk it from bottles, occasionally from a tap. When I was a kid I used to drink from the tap all the time. I’d run back into the flat all hot and sweaty from playing and didn’t even bother putting it in a glass, just turned the tap on and stuck my mouth underneath it. If my mum caught me doing it she used to scold me, but my dad just said that I had to be careful. ‘What if a fish jumped out?’ he used to say. ‘You’d swallow it before you knew it was there.’ Dad was always saying stuff like that and it wasn’t until I was seventeen that I realised it was because he was stoned all the time.

‘Stop that,’ I mumbled.

She gave me a pretty smile. ‘Stop what?’

I don’t mind getting drunk, but there always comes a moment in the evening when I find myself watching myself bumping into things and thinking, I’m bored of this, can I have full control of my brain back, please? I was getting equally irritated by my sudden need to deliver flowers to Hampstead and drink water from strange fountains. I tried to take a step backwards but the best I could manage was a minor shuffle.

Tyburn’s smile vanished. ‘Why don’t you have a nice drink?’ she asked.

She’d gone too far and she knew it, and she knew I knew she knew it too. Whatever influence she’d put on me must have been too subtle to handle a suggestion that obvious. Plus I’ve always wondered about that fish.

‘Good idea,’ I said. ‘There’s a pub down the road. Let’s go there.’

‘You cunning bastard,’ she said, and I didn’t think she was talking about me. She leaned in closer and stared into my eyes. ‘I know you’re thirsty,’ she said. ‘Drink the water.’

I felt my body lurch forward towards the fountain. It was involuntary, just like when you get a twitch in your leg or the hiccups, but now it was my whole body working to a purpose that wasn’t mine – it was terrifying. I realised then that the Old Man and Mama Thames hadn’t even been trying to control me and, had they wanted to, they could have had me doing cartwheels around the room. There had to be a limit to the power, or else what was to stop Mama Thames or the Old Man walking into Downing Street and dictating terms? I think people would notice if that happened – the Thames would be a lot cleaner, for a start.

It had to be Nightingale, I realised. The counterweight, the human balance to the supernatural, and that meant that they couldn’t control him. The only thing that separated Nightingale from an ordinary guy was his magic, which meant that the magic must supply a defence. It was a stretch, but it isn’t easy thinking things through when the personification of a historic London river is mentally trying to overwhelm you.

To try and buy time I attempted to throw myself backwards. It didn’t work, but it did stop my next lurch towards the fountain. Nightingale hadn’t taught me a block to the magic yet, so I reached for Impello instead. Lining up the forma in my mind was so much easier than I expected – later I speculated that whatever it was Tyburn was doing acted on the instinctive bit of my brain, not the ‘higher’ functions – that I got carried away.

‘Impello,’ I said, and tried to lift the statue off its pedestal.

Tyburn’s eyes widened at the sound of cracking marble. She whirled to look and as her eyes left mine I staggered back, suddenly free. I felt the shape in my mind slip out of control and the statue’s head disintegrated in a spray of marble chips. I felt a blow to my shoulder and a sharp cut on my face and a chunk of marble the size of a small dog slammed into the patio tiles by my feet.

I saw that the birdbath had also cracked, and that water was escaping and spreading across the patio like a bloodstain. Tyburn turned back to look at me. There was a cut on her forehead and her sundress was torn just above her hip.

She’d gone very quiet, and that was not a good sign. I’d seen that quiet before, on my mum and on the face of a woman whose brother had just been knocked down by a drunk driver. People are conditioned by the media to think that black women are all shouting and head-shaking and girlfriending and ‘oh, no you didn’t’, and if they’re not sassy then they’re dignified and downtrodden and soldiering on and ‘I don’t understand why folks just can’t get along’. But if you see a black woman go quiet the way Tyburn did, the eyes bright, the lips straight and the face still as a death mask, you have made an enemy for life: do not pass go, do not collect two hundred quid.

Do not stand around and try and talk about it – trust me, it won’t end well. I took my own advice and backed away. Tyburn’s black eyes watched me go, and as soon as I was safely in the side passage I turned and legged it as fast as I could. I didn’t exactly run down the hill to Swiss Cottage, but I did make it a brisk walk. There was a payphone near the bottom which I needed since the battery had been in my mobile during my statue demolition. I called the operator, gave my identification number and got a call routed to Lesley’s mobile. She wanted to know where I’d been because apparently it had all gone pear-shaped without me.

‘We saved the blind guy,’ she said, ‘no thanks to you.’ She refused to give me any details because ‘your boss wants you down here yesterday.’ I asked her where ‘here’ was and she told me the Westminster Mortuary, which made me cross because we may have saved the blind man but some poor bastard had still lost his face. I told her I’d be there as soon as possible.

I caught a lift in the local area car down to Swiss Cottage tube and hopped a Jubilee Line train into town. I doubted that Lady Ty had the manpower or the inclination to have the stations covered, and one of the few advantages of blowing out my phone was that it couldn’t be jacked, ditto any trackers she might have stashed about my person. I’m not being paranoid, you know. You can buy those things off the internet.

Rush hour was almost in full flood when I got on the train, and the carriage was crowded just short of the transition between the willing suspension of personal space and packed in like sardines. I spotted some of the passengers eyeing me up as I took a position at the end of the carriage with my back to the connecting door. I was sending out mixed signals, the suit and reassuring countenance of my face going one way, the fact that I’d obviously been in a fight recently and was mixed race going the other. It’s a myth that Londoners are oblivious to one another on the tube: we’re hyper-aware of each other and are constantly revising our what-if scenarios and counter strategies. What if that suavely handsome yet ethnic young man asks me for money? Do I give or refuse? If he makes a joke do I respond, and if so will it be a shy smile or a guffaw? If he’s been hurt in a fight does he need help? If I help him will I find myself drawn into a threatening situation, or an adventure, or a wild interracial romance? Will I miss supper? If he opens his jacket and yells ‘God is great’, will I make it down the other end of the carriage in time?

All the time most of us were devising friction-free strategies to promote peace in our time, our carriage and please God at least until I get home. It’s called, by people over sixty, common courtesy, and its purpose is to stop us from killing each other. It was like vestigia: you weren’t always aware of them but you instinctively shaped your behaviour in response to the accumulation of magic around you. This is what kept ghosts going, I realised; they lived off the vestigia like LEDs off a long-life battery, powering down to ration it out. I remembered the dead space that was the vampire house in Purley. According to Nightingale, vampires were ordinary people who became ‘infected’, no one was sure how or why, and started feeding off the magic potential, including the vestigia, of their surroundings.

‘But it’s not enough to sustain a living being,’ Nightingale had said. ‘So they go hunting for more magic.’ The best source of that, according to Isaac Newton, was human beings, but you can’t steal magic from a person, or any life more complex than slime moulds, except at the point of death and even then it isn’t easy. I’d asked the obvious question – why the blood-drinking? He said that nobody knew. I asked him why hadn’t anyone done any experiments, and he gave me a strange look.

‘There were some experiments done,’ he’d said after a long pause. ‘During the war. But the results were considered unethical and the files were sealed.’

‘We were going to use vampires during the war?’ I’d asked, and been surprised by the look of genuine hurt and anger on Nightingale’s face. ‘No,’ he’d said sharply, and then, with more moderation, ‘Not us – the Germans.’

Sometimes when someone tells you not to go somewhere it’s better not to go there.

The genii locorum, like Beverley, Oxley and the rest of the dysfunctional Thames family, were also living beings on one level, and also got their power from their surroundings. Bartholomew and Polidori both suggested that they drew sustenance from all the diverse and myriad life and magic within their domains. I was sceptical, but I was willing to accept that they lived in symbiosis with their ‘domains’, whereas vampires were clearly parasitical. What if that was mirrored by ghosts? If Thomas Wallpenny was in some way part of the vestigia he inhabited and drew power from, a symbiont, then the revenant could be a parasite, a ghost vampire. That would explain the shrunken cauliflower brains of the victims – they’d had the magic sucked out of them.

Which meant that the summoning I’d done with the calculators had achieved nothing more than to feed Henry Pyke’s appetite for magic. But I also wondered if you couldn’t attract a revenant by spilling magic around like laying a chum line for shark. By the time the train pulled into Baker Street, I was already beginning to formulate a plan.

The tube is a good place for this sort of conceptual breakthrough because, unless you’ve got something to read, there’s bugger all else to do.

This time when I arrived at Westminster Mortuary I didn’t even have to show my warrant card. The guards on the gate just waved me through. Nightingale was waiting for me in the locker room. While I was kitting out, I gave him a brief explanation of my meeting with Tyburn.

‘It’s always the children,’ said Nightingale. ‘They’re never satisfied with the status quo.’

‘How did you save the blind man?’ I asked.

‘Apparently they’re not blind,’ said Nightingale. ‘They are in fact visually impaired. A very forceful young lady pointed this out to me at some length while we were waiting at the hospital.’

‘How did you save the visually impaired man then?’

‘I wish I could take the credit,’ said Nightingale. ‘It was his guide dog. As soon the sequestration began …’

‘Sequestration?’ I asked.

Apparently this was the term Dr Walid had invented to describe what happened when a normal human being was taken over by our revenant. It’s a legal term that refers to the process by which a person’s property is seized in order to pay off debts, or because it’s considered to be the proceeds of crime. In this case the property sequestrated was the person’s body.

‘As soon as sequestration commenced,’ said Nightingale, ‘the guide dog, who I believe is called Malcolm, went berserk and dragged the potential victim away. Inspector Seawoll already had his people covering charity collections in the area, and one of them intervened before our poor sequestrated Punch could follow the blind man.’

‘Another triumph for intelligence-led policing,’ I said.

‘Quite,’ said Nightingale. ‘It was your friend Constable May who was on the scene first.’

‘Lesley? I bet she wasn’t happy about that,’ I said.

‘In her words: “Why does this shit always fucking happen to me?”’ said Nightingale.

‘So who was our sequestration victim when he was alive?’ I asked.

‘Who says he’s dead?’ said Nightingale.

He led me down the corridor, where they had a room kitted out as a mobile intensive care unit which is, when you think about it, a disturbing thing to find in a mortuary. Lesley was slumped in a chair in the corner of the room. She raised her hand in a hello when we entered. The bed was surrounded on both sides by machines huffing, going beep or just silently blinking. In the bed was Terrence Pottsley, aged twenty-seven, of Sedgefield, County Durham, a stock control manager for Tesco’s, next of kin most definitely not informed as yet. A thicket of stainless steel was growing out of his face – a medical scaffold they call it. Dr Walid hoped that would allow successful reconstructive surgery once the issue of Pottsley’s sequestration was resolved.

‘And I complained when I had my braces in,’ said Lesley.

‘Is he awake?’ I asked.

‘Apparently he’s being kept in what they call a “medical coma”,’ said Nightingale. ‘Did Oxley know who we’re dealing with?’

‘Isis did,’ I said. ‘She remembers Henry Pyke as a failed actor who may have been murdered by Charles Macklin – a much more successful actor.’

‘That would explain the resentment,’ said Nightingale.

‘Was he arrested?’ asked Lesley.

‘Records are sketchy,’ I said. ‘Pyke might have been arrested …’

‘Not Pyke,’ said Lesley. ‘Macklin. To get away with one murder is like an accident, but to get away with two seems a little bit fucking improbable. Not to mention unfair.’

‘Macklin lived on to a ripe old age,’ said Nightingale. ‘He was a fixture of Covent Garden life. I knew about the first murder, but I’d never heard of Henry Pyke.’

‘Can we have our discussion somewhere else?’ said Lesley. ‘This guy’s making me nervous.’

Since we were, mostly, coppers, that meant a pub or the canteen – the canteen was closer. I waited for Dr Walid to join us before outlining my strategy.

‘I have an idea,’ I said.

‘This better not be a cunning plan,’ said Lesley.

Nightingale looked blank, but at least it got a chuckle from Dr Walid.

‘It is, in fact,’ I said, ‘a cunning plan.’

Nightingale had been carrying around a hard copy of the Piccini script. I laid it out and drew attention to the scene that followed Punch’s disposal of the blind beggar. In it the constable arrives to arrest Punch for murdering his wife and baby.

‘I make myself the constable in the next scene.’

‘You’re volunteering to have your head beaten in?’ asked Dr Walid.

‘If you read the script you’ll see that the constable actually survives the encounter,’ I said. ‘As does the officer who arrives immediately after.’

‘I take it that would be me,’ said Nightingale.

‘Just so long as it’s not me,’ said Lesley.

‘I’m not sure I can see this working,’ said Nightingale. ‘Henry Pyke has no reason to engineer an encounter with us, however well we fit his little play.’

Dr Walid put his finger on the script and said, ‘Punch asks, “And who sent for you?” to which the constable replies, “I’m sent for you.” Punch doesn’t get a choice; this is his destiny catching up with him. “I don’t want the constable,” he says.’

‘I think you’ve got Punch all wrong,’ said Lesley. ‘You’re assuming he’s like a kind of supernatural serial killer who’s locked into acting out a Punch and Judy show. But what if he’s something else?’

‘Like what?’ I asked.

‘Like the manifestation of a social trend, crime and disorder, a sort of super-chav. The spirit of riot and rebellion in the London mob.’

We all looked at her in amazement.

‘You forget I did A levels too, you know,’ said Lesley.

‘Do you have another plan?’ I asked.

‘No,’ said Lesley. ‘I just want you to be careful. Just because you think you know what you’re doing doesn’t mean you actually know what you’re doing.’

‘I’m glad we’ve clarified that,’ I said.

‘You’re welcome,’ she said. ‘Even if you catch up with Henry, what then?’

It was a good question – I looked at Nightingale.

‘I can track his spirit,’ said Nightingale. ‘If I get close enough I can track him all the way back to his old bones.’

‘And then what?’ asked Lesley.

I looked at Nightingale. ‘We dig them up and grind them into dust, mix them with rock salt and then scatter them out at sea,’ I said.

‘And that’ll work?’ she asked.

‘Has before,’ said Dr Walid.

‘You’ll need a warrant,’ said Lesley.

‘We don’t need a warrant for a ghost,’ I said.

Lesley grinned and pushed the script over to my side of the table. She tapped the page with her spoon and I read the line: Constable: Don’t tell me. You have committed murder, and I have a warrant for you. ‘If you want to play the part, you’re going to need all the props.’

‘A warrant for a ghost,’ I said.

‘That at least will not pose a difficulty,’ said Nightingale. ‘Although it does mean we’ll have to postpone the capture operation until late tonight.’

‘You’re going ahead with this?’ asked Lesley. She looked at me with concern. I gave my best shot at insouciance, but I suspect it came out looking more like unfounded optimism.

‘I believe, Constable, that this is our only option,’ said Nightingale. ‘I’d be most grateful if you could brief Inspector Seawoll and ask him to stand ready in Covent Garden at eleven.’

‘As late as that?’ I asked. ‘Henry Pyke might not wait that long.’

‘We won’t get our warrant until eleven at the earliest,’ said Nightingale.

‘And if this doesn’t work?’

‘Then it’ll be Lesley’s turn to come up with a plan,’ said Nightingale.

We drove back to the Folly, where Nightingale vanished into the magic library, presumably to bone up on his revenant-tracking spells, while I went upstairs to my room and took my uniform out of the cupboard. I had to hunt around for my helmet, and eventually found it under the bed with my silver whistle, absurdly still part of the modern uniform, inside. Since my latest phone hadn’t survived Tyburn’s fountain I retrieved the police-issue Airwave from my desk and slotted in its batteries. As I packed it in my carryall with my uniform jacket I realised that the room still looked like somebody’s spare bedroom, somewhere I was just staying in until something better came along.

I slung the carryall over my shoulder and turned to find Molly watching me from the doorway. She cocked her head to one side.

‘I don’t know,’ I said. ‘But we’ll be eating out.’

She frowned.

‘I’m the one who’s going to be out front,’ I said, but it didn’t seem to impress her. ‘He’ll be fine.’

She gave me a last sceptical look before gliding away. By the time I was out of my room she was nowhere to be seen. I went downstairs and waited for Nightingale in the reading room. He emerged half an hour later dressed in his ‘working’ suit and carrying his cane. He asked me whether I was ready, and I said that I was.

It was a beautiful warm spring evening, so rather than take the Jag we strolled down past the British Museum before cutting through Museum Street and into Drury Lane. Even though we’d taken our time we still had hours to spare, so we popped into a curry house near the Theatre Royal, with the promising name of the House of Bengal, for dinner.

As I checked a menu mercifully free of potatoes, thick crust pastry, suet and gravy, I realised why Nightingale liked to eat out so much.

Nightingale had the lamb in wild lemon and I made do with a chicken Madras hot enough to make Nightingale’s eyes water. It was a little on the mild side for me. Indian cooking has no terrors for a boy raised on groundnut chicken and jelof rice. The motto of West African cooking is that if the food doesn’t set fire to the tablecloth the cook is being stingy with the pepper. Actually there’s no such motto – from my mum’s point of view it was simply inconceivable that anybody would want to eat anything that didn’t burn the inside of your mouth out.

We ordered a beer while we waited, and Nightingale asked me how my diplomatic efforts were progressing. ‘Leaving aside your little contretemps with Tyburn.’

I told him about the visit to Oxley’s river and Beverley’s response. I left out the whole wanting-to-jump-in-myself aspect of the visit. I said that I’d thought it had gone well, and had established that there was a mutual connection between the two sides. ‘It’s something we can build on,’ I said.

‘Conflict resolution,’ said Nightingale. ‘Is this what they teach at Hendon these days?’

‘Yes sir,’ I said. ‘But don’t worry, they also teach us how to beat people with phone books and the ten best ways to plant evidence.’

‘It’s good to see the old craft skills are being kept up,’ said Nightingale.

I sipped my beer. ‘Tyburn’s not a big fan of the old ways,’ I said.

‘Peter,’ he said. ‘Of all of Mother Thames’s children you had to pick a fight with Lady Ty.’ He waved his fork. ‘That is why we do not throw magic around until we are trained.’

‘What was I supposed to do?’

‘You could have talked your way out of it,’ he said. ‘What do you think Ty is – a gangster? Did you think she was going to “plug a cap” in your head? She pushed you to see where you’d go and you blew up.’

We ate our curries for a while. He was right – I’d panicked.

‘It’s “popped a cap in my ass”,’ I said. ‘Not plugged – popped.’

‘Ah,’ said Nightingale.

‘You don’t seem that worried about it, sir,’ I said. ‘The Lady Ty business.’

Nightingale finished a mouthful of lamb and said, ‘Peter, we’re about to offer ourselves up as Judas goats to a powerful revenant spirit who’s killed more than ten people that we know of.’ He dug into his rice. ‘I’m not going to worry about Lady Ty until after we’ve lived through that.’

‘If I remember rightly,’ I said, ‘I’m the Judas goat, the “constable” in this scenario. And considering that it’s my backside hanging out in the air, sir, are you sure you can track him?’

‘Nothing is certain, Peter,’ he said. ‘But I’ll do my best.’

‘And if we can’t run him into his grave?’ I asked. ‘Do we have a plan B?’

‘Molly can do haemomancy,’ said Nightingale. ‘It’s very impressive.’

I sorted through my slim store of Greek. ‘Divination through the agency of blood?’

Nightingale chewed thoughtfully and swallowed. ‘Perhaps that’s not the best term for it,’ he said. ‘Molly can help you extend your sense of vestigia out some distance.’

‘How far out?’

‘Two to three miles,’ said Nightingale. ‘I only did it the once, so it’s hard to tell.’

‘What was it like?’

‘Like stepping into a world of ghosts,’ said Nightingale. ‘It may even be the world of ghosts for all I know. It might be possible to find Henry Pyke that way.’

‘Why can’t we do it that way now?’ I asked.

‘Because the odds are five to one against you surviving the experience,’ said Nightingale.

‘So, yeah,’ I said. ‘Probably best not to do it that way now, then.’

If my profession – that’s thief catcher, not wizard – could be said to have started anywhere in London, then it started in Bow Street with Henry Fielding, magistrate, satirical author and founder of what came to be known as the Bow Street Runners. His house was right next door to the Royal Opera House, back when it was just the Theatre Royal and Macklin was supplementing his gin-running activities with a bit of acting on the side. I know all this because Channel 4 did a TV drama about it starring the bloke who played the Emperor in the Star Wars films. When Henry Fielding died, his position as magistrate was taken by his blind younger brother John, who strengthened the Bow Street Runners further but evidently not to the point where they could stop Macklin beating Henry Pyke to death practically on their doorstep. No wonder Henry was pissed off. I know I would be.

It became London’s first true police station, and in the nineteenth century it moved across the road and became the Bow Street Magistrates Court – probably the most famous court in Britain after the Old Bailey. Oscar Wilde was sent down there for being a public nuisance, and William Joyce, Lord Haw Haw himself, started his short walk to the hangman’s noose from Bow Street. The Kray twins were remanded there for the murder of Jack ‘the Hat’ McVitie. It was sold in 2006 to a land magnate who turned it into a hotel because while history and tradition have a fine voice in London, money has a sweet siren song all its own.

The original house had been replaced by an indoor flower market with an arched iron and glass roof. Eliza Doolittle, as played by Audrey Hepburn in My Fair Lady, would have bought her violets there before moving off to display the worst cockney accent this side of Dick Van Dyke. When they rebuilt the Royal Opera House in the 1990s it swallowed up most of the surrounding block, including the flower market. Which was why we found ourselves round the backstage entrance of the Opera House where, apparently, Nightingale knew a guy who could get us in.

It wasn’t so much a stage door as a heavy-goods entrance. I’ve seen warehouses with smaller loading bays, and there was an industrial-sized lift for getting enormous scenery palettes from floor to floor. Terry, a balding little man in a beige cardigan – Nightingale’s guy on the inside – said that they weighed upwards of fifteen tons, and when they weren’t being used were stored in a depot in Wales – he didn’t say why it had to be Wales.

‘We’ve come to see the Magistrate,’ said Nightingale.

Terry nodded gravely and led us through a series of narrow, white-painted corridors and HSE-specified fire doors that reminded me of uncomfortably of West-minster Mortuary. We finished up in a low-ceilinged storeroom that Nightingale assured us was the ground floor of the flower market.

‘Directly where the parlour of Number Four once stood,’ he said, and turned to our guide. ‘Don’t worry, Terry, we can see ourselves out.’

Terry gave us a cheery wave and left. The room was lined with ugly steel and hardboard shelving stuffed with cardboard boxes and delivery wraps full of napkins, cocktail sticks and packs of a dozen serving trays. The centre of the room was empty, with just a few scuff marks to show where a line of shelves had once stood. I tried to feel for vestigia but all I got at first was dust and ripped plastic. Then I sensed it, right on the edge of perception: parchment, old sweat, leather and spilled port.

‘A ghost magistrate,’ I said. ‘To provide a ghost warrant?’

‘Symbols have power over ghosts,’ said Nightingale. ‘They often have more effect than anything we can bring to bear from the physical world.’

‘Why’s that?’

‘To be honest, Peter,’ said Nightingale, ‘I remember the class where we studied it and I know I read the relevant passages in Bartholomew – I may even have written an essay, but I’m damned if I remember any of the why.’

‘How are you planning to teach me this stuff if you don’t know it yourself?’

Nightingale gently tapped his cane against his chest. ‘I was going to refresh my memory before we got to that part of your education,’ he said. ‘I know at least two of my Masters who did the same thing, and back then we had specialist teachers.’

I realised suddenly that Nightingale was looking for reassurance, which I found extremely worrying. ‘Just make sure you stay ahead of me,’ I said. ‘How do we find the Magistrate?’

Nightingale smiled. ‘We just need to get his attention,’ he said. He turned and addressed the empty centre of the room. ‘Captain Nightingale to see the Colonel.’

The smell of old sweat and spilled drink grew stronger, and a figure appeared in front of us. This ghost seemed more transparent than my old friend Wall-penny, thinner and more ghostly, but his eyes glittered as they turned on us. Sir John Fielding had worn a black bandage to hide his blind eyes, and Nightingale had called on the ‘Colonel’, so my guess that this was Colonel Sir Thomas de Veil – a man so routinely corrupt that he managed to shock eighteenth-century London society, generally considered by historians to be the most corrupt in the history of the British Isles.

‘What do you want, Captain?’ asked De Veil. His voice was thin and distant, and around him I could sense rather than see the faint outlines of furniture: a desk, a chair, a bookcase. Legend had it that De Veil had a special private closet where he conducted ‘judicial examinations’ of female witnesses and suspects.

‘I’m looking for a warrant,’ said Nightingale.

‘On the usual terms?’ asked De Veil.

‘Of course,’ said Nightingale. He drew a roll of heavy paper from his jacket pocket and proffered it to De Veil. The ghost reached out a transparent hand and plucked it from Nightingale’s fingers. For all that he did it casually, I was certain that the effort of moving a physical object must be costing De Veil something. The laws of thermodynamics were very clear on the subject – all debts must be paid in full.

‘And which miscreant are we looking to apprehend?’ asked De Veil, and placed the paper on the transparent desk.

‘Henry Pyke, Your Honour,’ said Nightingale. ‘Who goes by the name of Punch, and also by the name of Pulcinella.’

De Veil’s eyes glittered and his lips twitched. ‘Are we arresting puppets now, Captain?’

‘Let us say that we are arresting the puppet master, Your Worship,’ said Nightingale.

‘And the charge?’

‘Murder of his wife and child,’ said Nightingale.

De Veil tilted his head. ‘Was she a shrew?’ he asked.

‘I beg your pardon, Your Worship?’ said Nightingale.

‘Come now, Captain,’ said De Veil. ‘No man strikes his wife without provocation – was she a shrew?’

Nightingale hesitated.

‘A most terrible shrew,’ I said. ‘Begging Your Worship’s pardon. But the babe was an innocent.’

‘A man can be driven to terrible acts by the tongue of a woman,’ said De Veil. ‘As I can testify for myself.’ He winked at me and I thought, nice, there’s an image that will never fade. ‘However, the babe was innocent and for this he must be arrested and brought before his peers.’ A quill appeared in De Veil’s ghostly hand, and with a flourish he scratched out a warrant. ‘I trust you’ve remembered the prerequisite,’ said De Veil.

‘My constable will take care of the formalities,’ said Nightingale.

Which was news to me. I looked to Nightingale who made the Lux gesture with his right hand. I nodded to show that I understood.

De Veil made a show of blowing the ink dry before rolling the warrant into a tube and handing it back to Nightingale.

‘Thank you, Your Worship,’ he said, and then to me: ‘In your own time, Constable.’

I created a werelight and floated it over to De Veil, who cupped it gently in his right hand. Although I was still maintaining the spell the light dimmed as, I presumed, De Veil sucked up the magic. I kept it going for a minute before Nightingale made a cutting motion with his hand and I ended the spell. De Veil sighed as the light faded and nodded his thanks to me. ‘So little,’ he said wistfully, and vanished.

Nightingale handed me the roll of paper. ‘You are now duly warranted,’ he said. I unrolled the warrant and found, as I had suspected, that the paper was still blank. ‘Let’s go and arrest Henry Pyke,’ said Nightingale.

Once we were well clear of the storeroom I slapped the battery back into the Airwave handset and called up Lesley. ‘Don’t worry about us,’ she said. ‘We’re quite happy to be waiting around for you to get your finger out.’ Behind her I could hear voices, glasses and Dusty Small’s latest single. I didn’t have any sympathy; she was in the pub. I suggested that it might be time for her and the rest of the back-up team to go on standby.

Police work is all about systems and procedures and planning – even when you’re hunting a supernatural entity. When me, Nightingale, Seawoll, Stephanopoulos and Lesley worked out the details of the operation it took less than fifteen minutes because what we were doing was a standard identify, contain, track and arrest. It was my job to identify Henry Pyke’s latest victim. Once I’d done that, Nightingale would do his magic trick and track Henry’s spirit back to his grave. Seawoll’s people would provide containment in case things went pear-shaped, while Dr Walid stood by with a mobile trauma team to help any poor bastard who had the bad luck to have their face fall off. Meanwhile, DS Stephanopoulos was ready with a van full of builders on time and a half and, I found out later, a mini-JCB to dig up the grave wherever they might find it. She had another van full of uniformed bodies to handle crowd control in case Henry Pyke turned out to be buried under something inconveniently populated such as a pub or a cinema. Seawoll was technically in charge of the whole thing, which I’m sure put him in a wonderful mood.

Everything was supposed to be in place by the time Nightingale and I emerged from the Royal Opera House’s stage door and stepped back on to Bow Street. Given that Henry Pyke was beaten to death by Charles Macklin less than ten metres up the road, we both figured that this would be the ideal spot to start our little fishing expedition. Reluctantly I opened my carryall and donned my uniform jacket and my bloody stupid helmet. For the record, we all hate the bloody helmet, which is useless in a fight and makes you look like a blue biro with the top still on. The only reason we’re still wearing it is because the alternative designs all seem to be worse. Still, if I was going to act the part of a constable, I supposed I’d better look like one.

It was coming up to midnight, and the last of that evening’s opera devotees had trickled out of the House and headed for the tube station and taxi stands. Bow Street was as quiet and empty as any street in central London ever gets.

‘You’re sure you can track him?’ I asked.

‘You do your bit,’ he said, ‘and I’ll do mine.’

I tightened the strap on my helmet and checked in with the Airwave. This time I got Seawoll, who told me to stop faffing around and get on with it. I turned to ask whether I looked the part, which is how I came to be looking straight at the man in the good suit when he stepped out of the shadows by the stage door and shot Nightingale in the back.