‘Right, I think we should wait for a while, in case a student does want to speak to us, or in case Cassie comes back,’ Singh said. ‘I can’t quite read her. I don’t know if there’s actually anything useful she can tell us or not. I know Sasha said she had learning difficulties, but she comes across as quite astute to me. Could it all be an act?’

He looked at me as he asked this, suggesting it wasn’t a rhetorical question, but I shook my head. ‘I’m the wrong person to ask. Her BSL is a little bit below age appropriate, I’d say, but all that means is she might have some level of language delay, it doesn’t always point to learning difficulties. However, looking at it the other way around, if a student had learning difficulties, I would probably expect them to have some language delay. But I think you’d need an educational psychologist to answer that for certain. Could you ask to look at her school records?’ I suggested.

‘On what grounds, though?’ Singh asked. ‘No, I don’t think we can do that at the moment, we just need to keep an eye on her. A couple of the students mentioned her imaginary friend, but what if this is a real person? She’s claiming her friend is telling her not to talk to the police, and at first I wondered if this was a voice in her head, or if it was all just made up for attention, but I’m starting to think it could be an actual person who’s manipulating her.’

‘If Cassie’s “friend” told her to look for her phone in Steve’s office, it would make sense for them to be real,’ I said. ‘Why else would she break in there in the middle of the night?’

We thought about this as we waited, but no students appeared over break time, and when the next lesson started Singh wanted to get set up for some more interviews. I’d forgotten to charge my phone overnight, so while he was setting up I went back to my car for a portable charger I always kept in my glove compartment. As I shut the car door I saw a movement out of the corner of my eye. On the far side of the car park, I could see two people down the side of the residential block, an adult and a female student. A bolt of adrenaline shot through me and I headed towards them. Given what we’d learnt about safeguarding issues in the school, I wasn’t going to just sit there. Even if it was perfectly innocent, I knew that the students should have been in lessons.