Was I deliberately digging my own grave? Mills leapt on me. ‘So you admit you know the vicinity.’

‘I didn’t know Harriet lived there,’ I replied. ‘Until you told me.’

‘But you could have known. There was a feature on her in House & Garden magazine in January – three months ago. “A Great Place to Live”. It didn’t give the address, but they mentioned the area where she lived and they were stupid enough to show the front of the house, along with the number. So it wouldn’t have taken you long to track it down.’

‘Except that I’ve never read House & Garden.’

‘Did you have any contact with Harriet Throsby when she came to the Vaudeville?’ Cara asked. I should have recognised her technique. She was deliberately and very quickly changing the subject, giving me no time to think.

‘No.’

‘You didn’t shake hands – or embrace?’

‘No!’

‘Forensics found a hair on her blouse … the blouse she was wearing when she was killed. We’ve sent it for tests, but on first examination, it’s the same colour and length as yours.’

‘It can’t be mine,’ I said. ‘I never went anywhere near her. And I was nowhere near her house.’

‘You can say that now,’ Cara said. ‘But once we have a DNA match, it’ll all be over. And there’s something else. Show him, Derek.’

‘Yes, ma’am.’ Mills presented his next magic trick. This time I found myself looking at a black-and-white photograph of a man walking along the towpath next to the canal. The picture was taken by a CCTV camera and from behind, but I saw at once that the man had a very similar height and build to me. He was also wearing a grey puffer jacket with the hood up. I had a piece of clothing just like that.

‘This was taken at half past nine yesterday morning, approximately thirty minutes before Harriet Throsby was stabbed to death. The camera was positioned round the corner from where Ms Throsby resided, close to the Maida Hill Tunnel. Do you recognise the man in the picture?’

‘No.’

‘It looks very much like you.’

‘It can’t be me. At half past nine yesterday morning, I was in bed.’

‘But you have no witnesses to that. We only have your word for it.’

I had a sense of the clouds closing in and suddenly that twenty-four hours was looking more like twenty-four years. The weapon was mine. It had my fingerprints on it. A man very similar to me had been photographed in the area at the time of the murder. My hair was on the body. I had a motive: the bad review.

‘It will make this a lot easier for you if you confess,’ Cara Grunshaw said.

‘And the judge will take it into account too,’ Mills added.

They both sounded so reasonable.

‘Go to hell,’ I said. There was no point antagonising them, but I couldn’t stop myself. I’d had enough.

After that, I was taken back to the custody cell. I knew what was going to happen next. Cara was waiting until the DNA on the stray hair had been analysed by the laboratory and then, assuming there was a match with mine, she would charge me with murder. Was there any way one of my hairs could have ended up on the dead body of a theatre critic in Little Venice? It was impossible. I hadn’t come into contact with her at the theatre. And even if someone had set out to frame me, as Cara had suggested, there was surely no way they could have plucked it out of my head without my knowing.