It was a voice from an old London that no longer existed. It made the graph on the screens in front of Tara jump like lightning. When she looked up at us, Edie said, ‘So, Tara – what’s the difference between a lie detector and voice biometrics?’

‘Approximately the difference between a horse and a Ferrari,’ Tara said. ‘A polygraph – or lie detector – is hundred-year-old technology. It records physiological changes during questioning – blood pressure, breathing, heart rate, sweating and so on. And it’s fine if you are screening new employees. You’ll know if they’re lying about their CV, their qualifications and their smoking habits. But for someone like Paul Warboys? It just doesn’t work as well as it does in the movies. Someone like Warboys will be aware of what we call countermeasures. Confidence, controlled breathing, establishing a friendly – or at least a workable – rapport with the questioner. Confidence, above all. Not being scared by the process or his environment. That’s why a polygraph is not considered reliable evidence in a court of law. It is Jurassic technology. But voice biometrics does what we want a lie detector to do.’

We let her work. I stared down at the street, sipping a triple espresso from the Bar Italia until Tara Jones leaned back in her chair and ran her hands through her hair.

‘He’s telling the truth,’ she said.

*  *  *

In the afternoon Barry Wilder came in. There was no lawyer with him. But his wife Jean was there. She was waiting in the corridor outside the interview room with him, furiously stubbing out one unfiltered Camel on the floor and immediately lighting another one. Barry Wilder got to his feet at the sight of us, moving in weary slow motion, as if every movement took enormous effort.

‘There’s no smoking in this building, ma’am,’ Edie told his wife.

Jean Wilder glared at her and muttered under her breath as we went into the interview room.

‘Little ginger cow.’

Edie shook her head and let it go.

Barry Wilder eased himself into the chair opposite us.

‘OK,’ I said, ‘this interview is being recorded and may be given in evidence if any case is brought to trial. My name is DC Max Wolfe and I am currently serving with Homicide and Serious Crime Command here at West End Central, 27 Savile Row, London. The other officer present is DC Edie Wren. The time is 3 p.m.’ I nodded at Barry Wilder. If he had once been a man of violence then he looked as if all the violence had been knocked out of him.

‘Please state your name and profession.’

‘Barry Wilder. Builder.’

‘Thank you. Did you ever meet a man called Bert Page, Mr Wilder?’

He looked startled. ‘Who’s Bert Page?’

‘Bert Page was a war hero. Landed on Juno Beach on D-Day. Won the Distinguished Service Medal. Then, a lifetime later, Darren Donovan put him in a coma.’