‘I didn’t go near her.’

‘You may say that – but the trouble is, Grunshaw’s got enough evidence to hang you out to dry. And when the DNA results come in …’

‘It’s not my hair. It can’t be. I never went near her.’

‘That’s where you’re wrong, mate. I’ve already seen the analysis. It’s a definite match – 99.999 per cent probability.’

‘That’s impossible! Wait a minute …’ There were so many different thoughts in my head that they could have been having a massive punch-up, trying to get my attention. I played back what he had said. ‘How do you know that?’ I asked. ‘Cara hadn’t even seen the lab report. Do you know someone who works there?’

‘Not exactly …’ Hawthorne was being coy. There was something he didn’t want to tell me.

The answer arrived a moment later.

I noticed a movement at the door and, unannounced, Kevin Chakraborty came in. He was the teenager who lived with his mother in a flat one floor below. He was steering himself in the motorised wheelchair he was forced to use: he had been born with Duchenne muscular dystrophy, which, inch by inch, was stealing away his muscles and his ability to move. But as helpless as he might look to some, he was actually a brilliant computer hacker – whether it was my phone, the Police National Computer or the five million CCTV cameras across the UK. It would have been quite wrong to think of Kevin as disabled. He was one of the most spectacularly enabled people I had ever met.

‘Hello, Mr Hawthorne,’ he said. ‘I heard you arrive.’

‘No, you didn’t, Kevin. You’ve connected yourself to the video entry system and you watched us come in.’ Hawthorne was pleased to see him. ‘We were talking about you. Or I think we were about to.’

‘Kevin …’ I’d worked out exactly what had happened. ‘Have you hacked into the Metropolitan Police Forensic Science Laboratory in Lambeth?’ I demanded. I could have been a parent telling off a naughty boy.

‘It’s nice to see you, Anthony.’ Kevin was ignoring my question. He pushed the lever on his wheelchair and rolled towards me. ‘Mr Hawthorne told me you’d been arrested. I must say, I was jolly surprised. I never thought you had it in you to kill anyone.’

‘He says he’s innocent,’ Hawthorne said.

‘I got the DNA results,’ Kevin went on. ‘It’s a definite match. It’s your fingerprints too. I’ve got a photograph of them.’ The thing about Kevin was that he had a boyish enthusiasm for what he was doing and seemingly no awareness that it was a criminal offence. This, combined with his Bollywood good looks and, I suppose, the wheelchair, made it easy to forget how dangerous he was.

‘How long have we got?’ Hawthorne asked.

‘I took down their servers with a general denial-of-service attack,’ Kevin replied. ‘It means they’ve got the information, but they can’t access or share it—’

‘Wait a minute!’ I interrupted. ‘What exactly are you talking about?’ Then I remembered. ‘Cara said she had a computer problem. Was that you? What’s a denial-of-service attack?’