I nodded at the men, glad that they understood at last.

‘He’s not the one who bites,’ I said.

‘Let’s visit the dead,’ Mallory said at the morning briefing.

If you cut across St James’s Park it is a brisk ten-minute walk from 27 Savile Row to the Westminster Public Mortuary on Horseferry Road, and the Iain West Forensic Suite.

‘Iain West was the Elvis of forensic pathologists,’ Mallory told me as Gane, Whitestone and I struggled to keep pace with him. ‘A genius who changed everything. Proved WPC Yvonne Fletcher was shot from the Libyan Embassy. Located exactly where the Brighton bomb was placed in the Grand Hotel by interpreting the injuries of the victims. Examined the victims of the IRA atrocities at Harrods and Hyde Park. Single-handedly improved rail safety with his autopsies of the King’s Cross fire. And taught us all an invaluable lesson before dying while he was still a young man.’

‘What’s that, sir?’

‘The dead can’t lie.’

Deep inside the Iain West Forensic Suite we waited patiently in our blue scrubs and hairnets as Elsa Olsen, forensic pathologist, smiled and spoke with all the polite good grace of a hostess of a dinner party who was about to make the introductions.

Elsa had a lovely smile, I thought, as she turned her friendly gaze from our faces to the two naked corpses on the stainless steel tables before us.

‘Our mystery man,’ she said, indicating the drug-withered body of the homeless man. ‘Adam Jones. Born New Year’s Day, 1973. Died tenth of October 2008.’ She indicated his neighbour, the over-fed body of the banker. ‘And Hugo Buck, who I think you know already. Born on the seventh of January 1973, died ninth of October 2008.’

Elsa let the dates sink in. Mallory and I stared hard at the bodies. Born within seven days of each other. And died within twenty-four hours of each other. But what else connected them? Apart from the livid wounds that had opened up their throats, now gaping black slits, they looked as though they were from different planets.

Even in death, Hugo Buck’s body looked like that of a good amateur sportsman who was only just starting to run to expense-account fat. It was the body of a man who had serious gym sessions a few times a week, probably a personal trainer screaming at him for fifty quid an hour, no matter how busy he got at work; but the years were passing and there were plenty of meals at good restaurants during the working day, and a steady social drinking habit.

You wife-beating bastard.

In comparison, the shell of Adam Jones looked totally depleted, a pathetic sack of bones blotted with bad tattoos and veins scarred by damaged tissue – the squalid souvenirs of a thousand needles. He already looked on the cusp of old age, as if he had shot not just opiates into his veins but all his future years.

I shuddered.