‘Oh yes, you do,’ she insisted. ‘And so does your dog. Stan? Even if you don’t know it.’ She powered up her machine. ‘Two things. I’ve been running biometrics on the most recent film. The background sound is building work. I know, I know – all of London is a building site. But this is not the sound of someone having a loft conversion or a new conservatory put in. This is heavy machinery, a hundred and fifty feet below ground. That’s a major skyscraper going up. That narrows it down, doesn’t it?’

I nodded. ‘What’s the other thing?’

‘I did a review of your interviews with Mr Wilder and Mr Warboys. The interview with Mr Warboys has no biometrical anomalies. But I don’t think that Mr Wilder was telling you the whole truth.’

I remembered Barry Wilder in the interview room and my total conviction that he had been telling the truth. He had nothing to do with the lynching of Mahmud Irani.

‘I thought you said that voice biometrics was infallible?’

‘I never said infallible. I said that it was light years ahead of twentieth-century tech like the lie detector.’ She hit the keyboard and called up the interview tape. ‘Just watch, will you?’

I heard my voice.

‘Did you have contact with Mahmud Irani after he was released from prison?’

I heard Barry Wilder reply and saw a yellow line jump across Tara Jones’ screen like summer lightning.

‘Yes . . . I got a knife . . . I was planning to stick it in his heart.’

‘He’s telling the truth,’ I said.

‘Yes, but even when he’s telling the truth, his results show evidence of heart palpitations, raised blood pressure, shallow breathing. Initially I didn’t run tests on statements that we believed to be true. And I should have done.’

‘But he’s nervous,’ I said. ‘He’s in a police station. He’s admitting that he considered killing one of the men who abused his daughter.’

She shook her head. ‘It’s more than that. Far more. His blood pressure was a reading of systolic 190 over a diastolic 110 – that’s what doctors call a hypertensive crisis. Even when he was telling you the truth, his blood pressure was off the chart.’

‘Are you saying he lied to me?’

‘No,’ she said. ‘I’m saying that you didn’t ask him the right questions.’

*  *  *

Whitestone froze.

She was staring out at the massed reporters, photographers and camera crews stuffed into the first-floor media room at West End Central and they were all staring back at her, waiting for something to happen.

But nothing did.

This small, bespectacled woman, the most experienced homicide detective at 27 Savile Row, looked as if she did not understand what she was doing here, or what was expected of her. There was a statement in her right hand. I saw her fingers tighten into a fist, crumpling the statement.