‘We have forty people working on this case, and we’re looking at every possible angle and taking every phone call we receive very seriously. We’re working around the clock to find Yin, and we want to get her home as much as you do.’

She makes it sound like they can bring Yin home, like that’s still a possibility, but that can’t be true, can it? Not now. The hot prickles wrap around me and it’s unbearable but I stay still in this forest of alert green-and-orange backs and watch.

What I see is that Petra sits straightest of all in the front row, with her hands resting on a piece of paper covered with writing, staring at the policewoman like she would never break eye contact in a million years, not even if the room caught on fire. This is normal for Petra, because she is literally trying to hoover the knowledge from every corner of the room, all the time, and you can’t even stand near her for fear of your brain getting vacuumed. But there’s an extra level of hoovering today.

We’re all listening when the policewoman says, ‘I know you’ve been told not to talk to the media, so I have to tell you that some outlets will be running reports this week on something new. The police will be confirming at a press conference very soon that we’re looking for a serial offender.’

Petra jolts in her seat like she’s received an electric shock, but the rest of the class are a little more confused, looking at their friends, screwing up their faces.

‘What that means is that we’re now certain that we’re looking for someone who has done this before.’

That sets everyone whispering, wriggling, flapping. Celeste soldiers on calmly.

‘In the next few days we’ll be releasing a detailed profile of who we’re looking for, what this person might be like. What the media will say is that this person has to be connected with your school.’

Celeste scans the room, grave but calm. A buzzing noise builds in my head, threatening to drown everything out. I shouldn’t be confused at all because I remember what Ol’ X-Ray-Eyes Chapman said about the FBI and this is probably what he meant. A profile.

‘That connection is not confirmed. This person might be connected with Balmoral, maybe even very remotely connected, or they might have nothing to do at all with your school. We’re considering a large number of cases to determine if they’re linked. Are there any questions?’

Is it more likely that Yin is dead now, or less likely? Wasps are loose in the room.

Milla puts up her hand. ‘Why did you let the guy on the CCTV footage go?’

‘We investigated him thoroughly. He has no criminal record, a solid alibi for the night in question, and no unexplained absences.’