We reached the other side of the bridge and turned into the Strand. ‘Where were you this morning?’ I asked.

Hawthorne took a few more steps before answering. ‘I went over to Petty France,’ he said.

That was in Westminster. It was where a number of government offices were located. I remembered that the Passport Office had been in the same street, although even assuming they were still there, they would surely be closed on a Saturday. ‘Is that where you found the answer?’ I asked.

‘It was where I found what I expected to find.’

‘Well, I’m glad that’s sorted, then.’ I hated it when he was so cryptic.

The theatre was ahead of us. As far as I could see, the play was still running. In fact, there would be a matinée performance at three o’clock that afternoon. Hawthorne opened the front door for me. I went into the foyer …

… and stood there with my heart pounding, my stomach shrinking and a sense of complete despair as DI Cara Grunshaw and DC Mills lurched towards me. Grunshaw was grinning victoriously. Her assistant was contenting himself with an unpleasant smirk. They had both been expecting me.

‘So you kept your word,’ Grunshaw said. She was talking to Hawthorne.

‘Hawthorne—!’ I couldn’t believe he had done this to me.

‘I’m sorry, mate. Detective Grunshaw called me this morning. Somehow, she’d worked out where you were – which is surprising as working things out has never been her strong suit – and she made it clear to me. I can’t be seen to be obstructing the course of justice.’

‘But I thought we were friends!’

‘I’ll come and visit you in jail.’

‘I’m not going to jail. I didn’t kill anyone.’ I was close to tears. It wasn’t just the notion of being charged with a crime I hadn’t committed. It was Hawthorne lying to me, leading me into a trap.

‘I saw your play last night,’ Cara said. ‘I took Mills. What did you think of it, Derek?’

‘Not a lot,’ Mills said.

‘I quite enjoyed it myself. I think Harriet Throsby was very unfair. In fact, I might have been tempted to murder her myself if I’d been the writer. Anyway, shall we get the formalities over and done with?’

‘You do not have to say anything—’ Mills began. It was the second time he had given me an official police caution.

‘Hold on a minute,’ Hawthorne cut in. ‘I think you’re forgetting our deal, Cara.’

‘What deal?’ I grasped at the straw. Maybe they were going to let me run away.

‘Thirty minutes. I explain how it all happened. Then you make the arrest.’

‘We know how it happened,’ Cara growled.

‘That was still the deal we made.’

She sighed. Her ample chest rose and fell. ‘All right then, Hawthorne. But I haven’t got all day.’

‘Not here,’ Hawthorne said. ‘Inside.’

‘In the theatre? I didn’t have you pegged as a drama queen, but I don’t mind sitting down. I’ve been on my feet since breakfast and they’re killing me. Let’s get on with it.’