I stared at the cadavers. Mahmud Irani. Hector Welles. And Darren Donovan. Three men of wildly disparate ages, income and background. Irani had the soft spreading gut of a man who had spent a lifetime sitting down. Welles had been a confirmed fitness fanatic, spending hours pushing himself in parodies of manual labour. And Donovan had abused his body with Class A drugs since his early teens but still had the unearned slimness of youth.

Even their crimes were very different.

Irani had been one of a gang that abused vulnerable young girls for years. Welles, the heartless hit-and-run driver who was found wanting in a mad moment. And Donovan was a career junkie who regularly mugged elderly pensioners for his next shot of poison.

They did not look so different now.

Elsa considered the three of us shivering inside our blue scrubs and hairnets. On one side of me Edie Wren was impassive, her pale young face a mask of professional curiosity, but on the other side I could feel Dr Joe shaking with tension. It is never an easy thing to step inside the Iain West Forensic Suite for the first time.

‘So are you SIO on this investigation, Max?’ Elsa said.

‘Acting SIO,’ I said. ‘Until DCI Whitestone returns. Dr Joe’s with us looking for signatures, if that’s all right with you.’

The tall Norwegian pathologist nodded, anxious that she should only have to say all this once. She slowly circled the dead men on their stainless steel tables.

‘Life flows through the neck,’ she said. ‘The fragile, essential neck. Blood is pumped from the heart to the brain. Oxygen flows to the lungs. Compress the neck hard enough, and all that abruptly stops. You see the marks on their necks?’

On all three of them, the hanging mark angled diagonally across the neck, the highest point almost touching the left ear, where the noose’s knot had been. On all three men, the furrow of the hanging mark was far more shallow here. But it was pale yellow on Darren Donovan’s neck, a darker yellow on the raw skin of Hector Welles’ neck and a dark brown on Mahmud Irani, the earliest victim.

I felt the thick bile of revulsion rise up inside me and I swallowed it down. Deep breath, Max, I told myself. It’s about to get worse.

With a long thin stainless steel implement, Elsa gently prised open the mouth of Mahmud Irani. Then she did the same with Hector Welles, and finally Darren Donovan.

‘See that?’ Elsa said, her blue eyes bright. ‘When a man has been hanged, his tongue turns purple.’

Dr Joe had begun to pant like a dog on a summer’s day.

‘I’m OK,’ he said, not looking at me. ‘I’m fine. Really.’