‘How old are you?’

He cleared his throat and straightened his back again. Spoke for longer than it would take to give his age.

‘He says he’s nearly eleven,’ said Rima.

‘D’you live round here?’

‘York Square.’ He looked up at me through a thick forelock of almost-black hair. ‘My parent wait me there.’

‘In Limehouse?’

‘Yes.’

‘Who asked you to come here for the flash mob?’ I posed the question slowly, as I suspected he’d understand, and I wanted to gauge his reactions.

He waved his arms in the air, angrily, muttering in Arabic.

‘He says it wasn’t a flash mob. It was just a few people, dancing and playing music. He was here with a friend.’

He clenched a fist. Gabbled to Rima again.

‘He says they weren’t doing anything. Just passing time. They were bored. He says they’re The Street Rats.’

Ali laughed, pretending to be cocky. ‘Yeah. We are Street Rat.’ He winced as the movement tugged at the stitches in his forehead.

‘Is that a gang name?’

He jutted his jaw, defiance blazing in his eyes.

‘Do you need Rima to call your parents?’

‘Is OK. They wait me already.’

I needed to revisit a question. ‘We believe the flash mob was deliberately organised. Where did you hear about it?’

‘He can’t remember,’ said Rima.

‘We suspect that the fire at the shop was also caused deliberately. If that’s true, it’s a very serious offence.’ I softened my tone. ‘Especially if anyone has died.’

Ali looked at me now, and for the first time I noticed how black his eyes were. His shoulders were hunched, and he was jabbing at the floor with the heel of his shoe. I realised I felt scared for him. ‘Where did you hear about the flash mob?’

He began a lengthy explanation.

Rima translated as he spoke. ‘There’s a website that posts about upcoming events . . . some are flash mobs . . . the website tells you the date . . . and the rough location . . . you register your email or cell phone number . . . it’s called London for All. LfA, for short.’

‘And is the website public?’ A sinking feeling stole over me.

‘Yes, but they have a private discussion board,’ said Rima.

The news filled me with dread. Discussion forums were the bane of the police. ‘Do you know who runs the forum?’

He shook his head and spoke further.

‘A guy called Frazer,’ Rima translated, ‘ . . . posts the messages . . . but it’s never him that comes to the events . . . and no one knows who he is . . . it’s a different person . . . who comes along . . . and no one uses their real names on the forum.’

‘And what’s your username?’ I asked.

‘He says it’s “cookiemonster”.’

Ali blushed, and for a few moments, vulnerability betrayed his desire to look older.