Espress Oh! had an uninviting exterior which made the sign in the window claiming the ownership of ‘the best coffee in London’ seem a little unlikely. The door stuck slightly, eventually giving in and propelling Kelly inside with such force she almost fell over.

‘CCTV,’ she said to Nick triumphantly, pointing to the sticker on the wall that said Smile, you’re on camera! Inside, the café was much bigger than first appearances had suggested. Signs informed customers there was more seating upstairs, and a spiral staircase led down to what Kelly presumed were the toilets, judging from the steady stream of people going up and down them. The noise levels were high; conversations competing with the hiss of the vast silver coffee machine behind the counter. ‘We’d like to speak to the manager, please.’

‘You’ll be lucky?’ The girl on the till was Australian, her accent turning everything she said into a question. ‘If you need to make a complaint, we’ve got a form for it, yeah?’

‘Who’s in charge today?’ Kelly said, flipping open her warrant card so the badge was showing.

The girl didn’t seem fazed. She looked slowly and deliberately around the café. There were two other baristas, one wiping tables and the other piling coffee cups into an industrial dishwasher, with such speed and ferocity Kelly was amazed they didn’t shatter. ‘I guess that would be me? I’m Dana.’ She wiped her hands on her apron. ‘Jase, take the till for a bit? We can go upstairs.’

The first floor of Espress Oh! was filled with leather sofas that looked as though they should be comfortable, but were actually too hard and too shiny to want to settle into for long. Dana looked between Nick and Kelly expectantly. ‘What can we do for you?’

‘Do you have WiFi here?’ Nick asked.

‘Sure. Do you want the code?’

‘Not right now, thank you. Is it free for customers to use?’

Dana nodded. ‘We’re supposed to change the code every now and then, but it’s been the same for as long as I’ve been here, and the regulars like it that way. It’s a pain for them to keep asking for the code, and it makes more work for the staff, you know?’

‘We need to trace someone who’s logged on to your network here several times,’ Kelly said. ‘They’re wanted in connection with a very serious crime.’

Dana’s eyes widened. ‘Should we be worried?’

‘I don’t think you’re in any danger here, but it’s vital we track them down as soon as we can. I noticed on our way in you have CCTV – could we have a look at it?’

‘Sure thing. It’s in the manager’s office, through here.’ They followed her to a door on the other side of the room, where she pressed rapid numbers on the keypad fixed to the frame. She welcomed them into a room a little bigger than a broom cupboard, which housed a desk with a computer, a dusty printer, and an in-tray filled with invoices and delivery slips. On a shelf above the computer was a black-and-white screen showing a flickering CCTV image. Kelly recognised the counter they had seen upstairs, and the gleaming coffee machine.

‘How many cameras do you have?’ Kelly said. ‘Can we take a look at the other angles?’

‘It’s just that one, you know?’ Dana said.

As they watched, Kelly could see Jase, the lad Dana had handed over to, put a steaming latte on a black tray. It was just about possible to see a side view of his customer, before they turned away. ‘The only camera is pointing at the till?’ Kelly clarified.

Dana looked abashed. ‘The owner thinks we’re all on the take. It’s the same for the whole chain. We had a problem with antisocial behaviour last year and moved the camera to point at the front door. The boss went apeshit. Now we leave it be. Sleeping dogs, yeah?’

Nick and Kelly exchanged grim glances.

‘I’m going to have to seize whatever footage you’ve got from the last month,’ Kelly said. She turned to the DI. ‘Surveillance?’ He nodded.

‘We’re investigating a very serious offence,’ Nick told Dana, ‘and it may be we need to put in additional cameras for a few weeks. If that happens, it’s imperative your customers don’t know about it, which means,’ he gave Dana a serious look, ‘the fewer staff who know, the better.’

Dana looked terrified. ‘I won’t tell anyone.’

‘Thank you – you’ve been really helpful,’ Kelly said, although her heart was sinking. Every time she thought they had a strong lead on the offender behind the website, it collapsed into nothing. They could look at the CCTV footage at the times the offender used the WiFi connection to transfer his customers’ money, but with 90 per cent of the camera screen taken up with the staff and the till, their chances of getting a positive ID were tiny.

As they left the café, Kelly’s mobile beeped. ‘It’s from Zoe Walker,’ she said, reading the text. ‘She’s working from home for the foreseeable; just wanted to let me know she wouldn’t be on her office number.’

Nick shot her a warning look. ‘If she asks, there are no significant developments, okay?’

Kelly took a deep breath and tried to answer calmly. ‘I told Zoe how to access the website because I thought she had a right to see her own commute listed.’

Nick strode off towards the car, delivering his parting shot over his shoulder. ‘You think too much, PC Swift.’

Back in Balfour Street Kelly took the disk with Espress Oh!’s CCTV footage to the exhibits’ officer. Tony Broadstairs had more than twenty-five years as a detective on CID and MIT, and was fond of giving Kelly advice she neither wanted nor needed. Today he took it upon himself to outline the importance of the chain of evidence.

‘So you have to sign to say you’re passing this exhibit to me,’ he said, his pen drawing a circle in the air above the relevant section on the exhibit tag, ‘and I sign to say I’ve received it from you.’

‘Got it,’ nodded Kelly, who had been seizing and signing for exhibits for the last nine years. ‘Thanks.’

‘Because if one of those signatures is missing, you can kiss goodbye to your case at court. You can have the guiltiest man in the land, but once the defence get wind of a procedural cock-up, it’ll collapse faster than a soufflé taken out of the oven too early.’

‘Kelly.’

Turning round, Kelly saw DCI Digby walking towards them, still wearing his overcoat.

‘I didn’t realise you were in, sir,’ Tony said. ‘I thought you were still using up all that leave you’ve accrued. Didn’t fancy golf today, then?’

‘Trust me, Tony, I’m not here out of choice.’ He looked at Kelly, unsmiling. ‘My office, now.’ He called across to the DI. ‘Nick, you too.’

The relief Kelly felt at no longer having to listen to Tony’s lesson in exhibit-handling was swiftly tempered by the look on the DCI’s face. She scurried after him across the open-plan space to his office, where he threw open the door and told her to sit down. Kelly did so, a feeling of dread creeping over her. She tried to think of some other reason why the DCI would have hauled her so unceremoniously into his office – and indeed come in on his rest day to do so – but kept returning to the same thing.

Durham.

She’d really fucked up this time.

‘I went out on a limb for you, Kelly.’ Diggers had stayed standing, and now he strode from one side of the tiny room to the other, leaving Kelly unsure whether she should keep her eyes on him, or stay facing forward, like a defendant in the dock. ‘I agreed to this secondment because I had faith in you, and because you convinced me I could trust you. I fought your bloody corner, Kelly!’

Kelly’s stomach clenched with fear and with shame; how could she have been so stupid? She’d hung on to her job by the skin of her teeth last time; the suspect she’d flown at had decided against pressing criminal charges, after a visit from Diggers persuaded him he didn’t want to be in the spotlight any more than was necessary. Even the disciplinary hearing had gone in her favour, thanks to Diggers having another quiet chat with the superintendent. Mitigating circumstances due to family history, the report had read, but she’d been left in no doubt it was a card she couldn’t play twice.

‘I got a phone call last night.’ The DCI finally sat down, leaning forward across the expanse of dark oak desk. ‘A DS from Durham Constabulary, alerted to the fact that we’d been enquiring about historical rapes. Wondered if they could help any further.’

Kelly couldn’t meet his eyes. To her left she could feel Nick looking at her.

‘Of course, this came as rather a surprise to me. I might be counting down to retirement, Kelly, but I like to think I still know what jobs the office is dealing with. And none of them,’ he slowed his speech, pausing between each word for added emphasis, ‘relates to Durham University. Would you care to explain what the hell you’ve been doing?’

Slowly, Kelly looked up. The blind rage that had consumed Diggers seemed to have blown itself out, and he looked less terrifying than when he had first started. Even so, Kelly’s voice shook, and she swallowed hard in an attempt to get herself under control.

‘I wanted to find out if there had been any developments on my sister’s case.’

Diggers shook his head. ‘I’m sure I don’t need to tell you that what you’ve done represents a serious disciplinary offence. Quite apart from the criminal implications of breaching the Data Protection Act in this way, abusing your position as a police officer for personal gain is a sackable offence.’

‘I know that, sir.’

‘Then why on earth …?’ Diggers spread his hands wide, his face registering total incomprehension. When he spoke again, it was softer. ‘Have there been any developments in your sister’s case?’

‘Sort of. Only not the kind I expected, sir.’ Kelly swallowed again, wishing the hard lump in her throat would go away. ‘My sister … she’s withdrawn support for the prosecution. She’s left explicit instructions that she doesn’t want to be kept informed of any developments, and has no wish to know if the offender is ever arrested.’

‘I take it this was news to you?’

Kelly nodded.

There was a long pause before Diggers spoke again.

‘I think I know the answer to this already, but I have to ask: is there any professional reason for you making such a request to another force?’

‘I asked her to,’ Nick said. Kelly turned to look at him, trying to conceal her shock.

‘You asked Kelly to contact Durham about a historical rape involving her sister?’

‘Yes.’

Diggers stared at Nick. Kelly thought she saw amusement in his eyes, but his mouth was set hard and she decided she was imagining it. ‘Would you care to explain why?’

‘Operation FURNISS has proved to be more wide-ranging than first anticipated, sir. The Maidstone rape indicated that offences aren’t confined to within the M25, and although the adverts only started in September the full extent of the crimes aren’t yet clear. We’ve so far struggled for leads on the principal offender and I thought it would be a good idea to take a broader look at rapes with a history of stalking. I thought it possible the pattern might have been repeated in other cities.’

‘Over a decade ago?’

‘Yes, sir.’

Diggers took off his glasses. He eyed Nick thoughtfully, then looked at Kelly. ‘Why didn’t you tell me this in the first place?’

‘I – I’m not sure, sir.’

‘I take it you haven’t found a link between Operation FURNISS and Durham?’ The question was directed at Kelly, but it was Nick who answered.

‘I’ve ruled it out,’ he said, without any of Kelly’s hesitation.

‘I thought as much.’ Diggers looked from Kelly to Nick and back again. Kelly held her breath. ‘Might I suggest we consider the background research into similar crimes complete?’

‘Yes, sir.’

‘Get back to work, the pair of you.’

They were in the doorway when Diggers called to Kelly. ‘One more thing …’

‘Sir?’

‘Offenders, coppers, witnesses, victims … there’s one common thread running through them all, Kelly, and it’s that no two people are the same. Every victim deals differently with what’s happened to them; some are hell-bent on revenge, others want justice, some are looking for closure, and some’ – he looked her straight in the eye – ‘some just want to move on.’

Kelly thought of Lexi, and of Cathy Tanning’s desire to start over, in a house to which no one but her had the keys. ‘Yes, sir.’

‘Don’t get hung up on the victims who want a different outcome to the one we want. It doesn’t make them wrong. Focus that drive of yours – your not inconsiderable talent – on the case as a whole. Somewhere out there is a serial offender responsible for the rapes, murders and stalking of dozens of women. Find him.’