The next morning I got up late, so I was still in my pyjamas when Singh rang and asked me to meet him at the police station. I reminisced briefly about my days working for an agency when I knew in advance what jobs I was going to have each day, but on the other hand I genuinely loved working with the police. I felt like I was actually doing something worthwhile.

When I arrived, Singh met me in the lobby and took me through to an interview room, where Sasha Thomas was sitting next to Cassie. Sasha smiled at me and gave me a nod. A moment later, DI Forest walked in and we were ready to begin.

‘Cassie, you and Sasha have come up here this morning because there is something we need to talk to you about,’ Singh explained, his face grave.

The girl fidgeted in her seat as the DS continued. ‘We have had our computer experts looking at your school systems, and they’ve found some messages between you and a member of staff.’

Cassie’s face drained of all colour and she stopped moving, staring at Singh.

I don’t know what you mean.

‘There are lots of messages between your school computer account and a staff account. They talk about the other students, and Joe. They go right back to when Ms Villiers left the school. The messages stopped in September, when you and the others got your secret phones.’

Sasha’s face was ashen as she watched Cassie for a reaction. The pause before Cassie replied felt like it stretched on for days.

I don’t know what you mean, the girl repeated, looking down at her feet.

Forest sat back and folded her arms. ‘Lying to us won’t help you, Cassie. We’ve read the messages. You knew this person was pretending to be Joe, and messaging all your friends. They told you to pretend you got messages as well.’

Cassie looked around the room for a moment, then looked at Sasha. Am I going to get in trouble?

Sasha shook her head slowly. Just tell the truth. Right now, that’s the most important thing.

I didn’t want Mike to get hurt, Cassie said, anxiety shining on her face. My heart sank at the idea that this young girl was under his spell. I was sure he wouldn’t get involved with a child, however mature she looked, but that didn’t mean he wouldn’t find other ways to manipulate her.

‘Was Mike the person you were messaging?’ Singh asked, and only then did I realise they didn’t know who the staff member was.

What? No! It can’t have been him, Cassie replied, sitting forward and giving the detectives an anxious look.