I’m not sure what will happen. The machine seems to hang, to take an age, but then the screen changes and a message appears across its centre.

‘Welcome back, Katie. It’s been a while!’

It feels as if something has struck me, slammed me back to earth. I’m winded, I can’t breathe, but then I realize the message is automated. I breathe deeply, try to calm down. Next to it there’s a button marked ‘Enter’. I press it.

I’m not ready for what I see; there’s a picture of my sister, in the top-left corner of the screen beneath the website’s logo. It jolts me again. It’s like she’s there, sitting at her computer. It’s as if all I have to do is type a message and press send – just like I can with Anna, and Adrienne, and Dee and Fatima – and then I’ll be able to talk to her again, tell her I’m sorry, that Connor is safe. That I miss her.

But I can’t. She’s gone. I focus on why I’ve logged on here, I make myself look at the photo she used. It looks like it was taken on a holiday. It’s a close-up. She’s lying on a beach towel, on her front, reading a book. Her sunglasses are pushed back on her head, her skin is tanned. She’s wearing a bikini and has hoisted herself up on her elbows. Her breasts push up against the fabric of the towel, yet it looks unposed, natural.

She’s smiling. Happy. I stare at the picture. I wonder when it was taken, and by whom. She looks so relaxed. I can’t believe the little girl I’d once held, once bathed, once read to, is gone. I can’t believe I’ll never speak to her again.

I begin to cry. I’m sliding, backwards, towards pain. I can’t do this, I think. Not alone.

I call Anna back.

‘There should be a tab at the top for recent activity. You could look there. It lists the last few people who have looked at her profile.’

She’s already asked me if I’m all right, what I’m up to. She’s already questioned whether this is a good idea and I told her the half-lie that Adrienne had suggested it. ‘I just want to see if there’s anything the police might’ve missed.’

‘Right. Got it.’

‘Then you should see the rooms. On the right?’

I minimize the chat window and Anna’s face disappears. Behind it is the dating site, the list of chatrooms. Looking for Love? Something Extra. A Bit on the Side. Couples and Groups. I wonder which one Kate would have gravitated towards.

‘Okay.’

‘Kate and I used to go to Casual Chat,’ says Anna. ‘But there should be a tab, at the top. Friends and Favourites.’

‘I see it.’

‘They’re the people Kate was chatting to. The ones she’s connected with, linked her profile to.’

I click on the tab and the page changes. A list of names appears, with thumbnail photographs. I freeze. My right hand begins to shake. Robbie676, Lutture, SteveXXX … this list goes on.

I scroll down; there are about fifteen names in total.

‘Anything?’ says Anna.

My hope floods away and I’m suddenly empty. Hollowed out. This is futile, and I’m an idiot. What did I think I’d see? A message from one of her friends, telling me he killed my sister? A message to her: ‘I got you in the end’?

‘I don’t know. Just a list of names. They could be anyone.’

She says nothing.

I realize for the first time that she might be scared. She’s been on the same site, possibly even talking to the same people. She must be thinking how easily it might have been her in that alleyway instead of Kate.

For a moment I wish it had been, but then I push that thought away. I don’t wish that, not on her, not on anyone.

‘Maybe you should look at some of them?’ she says. ‘Their profiles? Find out if any live nearby.’

I’m surprised. ‘Won’t they all?’

‘Not necessarily. Don’t forget, Kate wasn’t only interested in meeting up with people in the real world. With some of them it was all virtual. They might be anywhere, on the other side of the planet.’

She’s right, of course. I select a couple of the profiles to look at in detail. SexyLG, whose profile picture is of a sunset, lives in Connecticut; CRM1976, it turns out, is a woman. I click on a few more and find that most seem to live abroad – in Europe, the States, Australia. Some are much older than Kate, a couple younger. None looks like the kind of person I imagine Kate being interested in, sexually or otherwise.

‘Anyone?’

‘Not yet. I need to look in more detail.’

I scan through the rest. I can see only one who fits the bill. Harenglish.

‘Here’s one. Male, lives in Paris.’ I click on his profile. He’s used a head-and-shoulders photo, and is bald. He wears glasses and a leather motorcycle jacket. He’s hidden his age but looks as though he’s in his mid- to late thirties. He’s a Pisces, he says, single, looking for love or ‘fun along the way’.

‘What’s he called?’ says Anna. I tell her, and then hear her typing. I guess she’s logging on to the same site, searching for his profile.

I stare at his picture as if it’s a puzzle I need to solve. He looks nice enough, sort of innocent, but then what does that even mean? Anyone can find a decent picture of themselves, anyone can present themselves in the best light. Isn’t that what we’re all trying to do, on some level? Show our best face to the world, leave the darkness within? The screen of the internet just makes it easier.

If only there were some way I could find out how well he’d known my sister. If they’d been close enough that she’d listed him as a friend, why hasn’t he messaged her, why hasn’t he expressed shock, or at least surprise, when she disappeared?

‘I don’t recognize him.’

I imagine doing what Adrienne suggested. Taking down his name, along with any more that look as if they might be people Kate had met, then handing the information over to the police. But maybe they’ll have looked at these names already.

‘I’m going to message him.’

‘Wait!’ There’s an edge in her voice; it’s alarming, surprising. I open her Skype window; her eyes are narrowed as if she’s concentrating, she looks anxious.

‘What is it?’

‘That might be dangerous. I mean, think about it. You’re logged on with Kate’s profile. If it is him who killed her he’ll know you must be someone else, pretending to be her. It’ll just drive him underground. We have to be clever about this.’ She hesitates. ‘Maybe I should send him a message? Say hi. See if I can find anything out.’

I hear her begin to type. ‘Sent,’ she says after a few seconds, and as she does my machine pings with a message. It’s not from her, though, and neither is it from Harenglish. Someone else has messaged Kate. Eastdude.

There’s a peculiar rush of excitement, one I wasn’t expecting.

‘I’ve got a message!’

‘Who from?’

I tell her. The name’s familiar. I open the list of usernames Kate had tucked into her Filofax and see that I’m right. It’s there.

‘This guy’s on Kate’s list. It’s him.’

‘Julia, we don’t know that.’

She’s right. Even as I begin to argue, I realize my logic is flawed. If he’s killed my sister, why would he be messaging her now?

I stare at the message as if it’s dangerous, poisonous.

‘Maybe he just wonders why Kate’s been so quiet.’

‘I’m going to read it.’

I click on Eastdude’s message and it opens in a new window. It looks as though it’s been typed hurriedly. ‘Hey katie. You’re back! Missed u! If u fancy another hook up – I’m still up 4 it!’

I try to imagine what Kate would’ve done. Would she have just sent a reply, a yes? And after that? They’d arrange a date, I suppose, they’d meet up. Drinks and dinner? Or would she have just gone to his place, or had him round to hers? Would it be simpler just to cut out the preliminaries?

‘He wants to know if she wants to hook up.’

‘Hook up where?’

‘He doesn’t say.’ I click on his profile. He’s in his early thirties, he says, though the photo suggests an extra ten years at least. Under ‘Location’ he’s written ‘New York’.