He tried to stick his pencil in his nose. His ear. His mouth. I crouched next to him and moved his stiff little fingers into the correct position. Beside me, Phoebe Canning studied him with interest. She was a sturdy redhead who claimed to be Aaron’s best friend. I’d already identified her as a bit of a queen bee; she’d been telling the other kids what to do, her authority derived from an older sister in year five.

‘Look, Aaron,’ she said. ‘You should hold it like this.’

Aaron scowled. Then he jabbed her with his pencil.

‘Ow!’ Her squeal made everyone glance up. ‘You hurt me!’

‘Aaron. If you’re angry, use your words. Don’t hurt people.’ I was thinking of the form I would have to fill in.

‘I’m not your friend anymore.’ Phoebe grabbed her drawing. ‘I’m going to sit next to Kayla.’

Aaron threw down his pencil and bolted. But he didn’t leave the room. I had enough time to soothe the jangled nerves of the other kids before approaching him in the corner where he was squatting, his back to the class, his head bent over something that made my heart sink.

‘What have you got there?’ I said, though I could see it was a brown Swiss Army knife.

‘Dad gave me it.’ His voice was low and hoarse.

Great, I thought, filing that away for later. ‘How does it work?’

Aaron showed me. He pulled out the corkscrew, the hook, the scissors. I nodded, keeping one eye on the rest of the class. Then I asked if I could try.

‘No,’ he said.

‘Please? I want to see if I can do it.’

He looked confused. But he surrendered the knife, and when I pretended to struggle with it, he helped me.

That was good.

By now the other kids were getting interested. Some of them were sliding off their chairs. I lowered my voice and told Aaron I needed to borrow his knife for a while. ‘I’ll give it back,’ I promised. ‘When school’s finished.’

Aaron frowned. Something sparked in his eyes. Panic? Fury? But before I could continue, the bell rang.

‘It’s recess!’ Phoebe announced. ‘We can go play!’

The stampede nearly bowled me over. I had to jump up and wade in. Aaron was so eager to leave that he forgot about his knife. I tucked it into my pocket and made another mental note. Lock it up.

There was a rule about bringing favourite toys to school—especially if you could kill people with them.

The juniors at Otford primary were corralled into a special part of the playground. They had their own monkey bars, drinking fountains and nubbly expanse of softfall rubber. If they were scared of the bigger kids, they could always find a place to hide.