‘What does that mean?’ Connor asked.

‘That he’s not wearing the Fitbit now,’ Pip said. ‘Or it hasn’t been in the proximity of his phone to sync the data.’

But when she skipped past Sunday and Saturday and clicked on to the Friday he went missing, the icons burst into life, completed circles in thick bands of green and orange. And those words were gone, replaced by numbers: 10,793 steps walked that day, 1649 calories burned. A heart rate graph that spiked up and down in bright blocks.

And Pip felt her own heart react, taking over, pulsating inside her fingers as it guided them along the mousepad. She clicked on the step count icon and it brought up a new screen, with a bar-chart breakdown of Jamie’s steps throughout the day.

‘Oh my god!’ she said, eyes on the very end of the graph. ‘There’s data here from after the last time Jamie was seen. Look.’ She pointed to it as Joanna and Connor drew closer still, eyes spooling. ‘He was walking, right up until midnight. So, after 11:40ish when he was seen on Wyvil Road, he did . . .’ She highlighted the columns between 11:30 p.m. and 12:00 to work out the specific number. ‘One thousand, eight hundred and twenty-eight steps.’

‘What distance is that?’ Joanna asked.

‘Just googling it,’ Connor said, tapping at his phone. ‘That’s just under a mile.’

‘Why does he stop suddenly at midnight?’ said Joanna.

‘Because that data falls under the next day,’ Pip said, pressing the back arrow to return to Friday’s dashboard. Before she flipped to Saturday instead, she noticed something in Jamie’s heart rate graph and clicked the icon to zoom in.

It looked like Jamie’s resting heart rate was around eighty beats per minute, that’s where it stood for most of the day. Then at half five, there was a series of spikes up to around one hundred beats per minute. That’s when Jamie and his dad had been arguing, according to Connor. It settled again for a couple of hours, but then started to climb back up through the nineties, as Jamie was following Stella Chapman, waiting to talk to her at the party. And then it got faster, during the time when George saw Jamie on the phone outside, most likely to Layla. It stayed at that level, just over a hundred, as Jamie walked. Beyond 11:40 p.m. when he was seen on Wyvil Road, his heart steadily grew faster, reaching one hundred and three at midnight.

Why was it fast? Was he running? Or was he scared?

The answers must lie in the early hours of Saturday’s data.

Pip switched over to it and immediately the page felt incomplete compared to the day before, coloured circles barely filled in. Only 2571 steps in total. She opened the step-count menu out fully and felt something heavy and cold dragging her stomach into her legs. Those steps all took place between midnight and around half past, and then . . . nothing. No data at all. The graph completely dropped off: an entire line of zero.

But there was another shorter period within that, where it looked like Jamie had taken no steps. He must have been standing still, or sitting. It happened just after midnight, and Jamie didn’t move for a few minutes, but it wasn’t for long because just after five past, he was on the move again, walking right up until the point where everything stopped, just before 12:30 a.m.

‘It just stops,’ Connor said, and that far-away look was back in his eyes.

‘But this is amazing,’ Pip said, trying to bring his eyes back from wherever they’d gone. ‘We can use this data to try track where Jamie went, where he was at just before half twelve. The step count tells us that that’s when the incident, whatever it was, happened, which fits, Joanna, with your text at 12:36 never delivering. And it might also tell us where it happened. So, from 11:40, when he’s seen at the bend in Wyvil Road, Jamie walks a total of two thousand and twenty-four steps before he stops for a few minutes. And then he walks another two thousand three hundred and seventy-five, and wherever that takes him is right where whatever happened, happened. We can use these figures to draw up a perimeter, working from that last sighting on Wyvil Road. And then we search within that specific zone, for any sign of Jamie or where he went. This is good, I promise.’

Connor tried a small smile, but it didn’t convince his eyes. Joanna also looked afraid, but her mouth was set in a determined line.

Pip’s phone rang in her pocket again. She ignored it, navigating back to the dashboard to look at Jamie’s heart rate in that time span. It started already high, above one hundred, and, strangely, in that window of a few minutes when he wasn’t moving, his heart was picking up faster and faster. At the point right before he started walking again, it spiked up to one hundred and twenty-six beats per minute. It trailed off, but only slightly as he walked those additional two thousand three hundred and seventy-five steps. And then, in those last couple of minutes before half past the hour, Jamie’s heart peaked up to one hundred and fifty-eight beats per minute.

And then, it flatlined.

Dropped from one hundred and fifty-eight straight to zero, and beat no more after that.

Joanna must have been thinking the same thing because just then, a gasp, wretched and guttural, ripped through her, hands smacking to her face to hold everything in. And then the thought took Connor too, his mouth hanging open as his eyes flickered over that steep fall in the graph.

‘His heart stopped,’ he said, so quietly that Pip almost didn’t hear him, his chest juddering. ‘He’s . . . is he . . .’

‘No, no,’ Pip said, firmly, holding up her palms, though it was a lie, because inside she was feeling the same dread. But she had to hide hers, that’s why she was here. ‘That’s not what it means. All this means is that the Fitbit was no longer monitoring Jamie’s heartbeat data, OK? Jamie could have taken the Fitbit off, that’s all this could be showing us. Please, don’t think that.’

But she could see from their faces that they weren’t really listening to her any more, both of their gazes fixed on that flatline, sailing along with it into nothingness. And that thought – it was like a black hole, feeding on whatever hope they had left, and nothing Pip could say, nothing she could think of to say, could possibly fill it in again.

I almost had a disaster, when I remembered you can’t get into DMs on the desktop version of Instagram, only on the mobile app. But it’s OK: Jamie’s associated email was still logged in on his laptop. I was able to send a reset password request from Instagram and then sign into Jamie’s account from my phone. I went straight to Jamie’s DMs with Layla Mead. There weren’t too many of them; only over the course of about eight days. Judging from context, it looks like they met on Tinder first, then Jamie moved the conversation to Instagram and then they moved on to WhatsApp, where I can’t follow them. The start of their conversation:

Found you . . .

so you did. i wasn’t exactly hiding

from you : )

how’s your day been?

Yeah it’s been good, thanks. I just made the best

dinner this world has ever seen and I might

possibly be the greatest chef.

And humble too. Go on, what was it?

Maybe you can make it for me some day.

I fear I may have talked this up a bit much.

It was essentially mac and cheese.

Most of their messages are like that: long bouts of chatting / flirting. On the third day of messages, they discovered they both loved the show Peaky Blinders and Jamie professed his lifelong ambition to be a gangster from the 1920s. Layla does seem very interested in Jamie, she was always asking him questions. But there are a few strange moments I noticed: