If you have a cardiac arrest in London – or if your heart rate has fallen off a cliff because you are freezing to death – then paramedics and ambulance technicians have the authority to bypass the nearest Accident and Emergency department and take you directly to one of eight specialist heart attack centres, immediately doubling your chances of survival.

And that’s what they did with Hana.

The ambulance sped north and I stayed by her side until she was rushed into the Intensive Care Unit at the Royal Free in Hampstead. And then I waited. After I had downed two cups of scalding black coffee, a doctor came out to see me, a young man of around thirty who looked as though he hadn’t slept since leaving medical school. Dr Patel, it said on his name tag.

He glanced at my warrant card and nodded.

‘Do we have a name for the victim, DC Wolfe?’ he said.

‘I only know her first name,’ I said. ‘Hana.’

‘Hana has severe hypothermia. Which is easy to diagnose and hard to treat. She’s suffering from what we call afterdrop – her core temperature is continuing to fall after removal from cold stress. And her core temperature is likely to drop for the next few hours. We are going to give her a heart-lung bypass where we withdraw blood from the body, warm it up and return it to the body. She’s on a CPB pump to maintain blood circulation and keep her oxygenated.’ He paused. ‘Do you know how long she was exposed to sub-zero temperatures? Anything at all about her medical history?’

I shook my head.

‘When can I talk to her?’

He looked at me as if I still didn’t quite get it.

‘Hypothermia is next door to death, Detective – it suppresses heart and brain function and the internal organs all stop working. Do you understand? Everything that keeps you alive suddenly stops.’ He ran a hand through his already thinning hair. ‘We’re not even allowed to declare someone dead until their body is warmed to a near normal body temperature.’

And finally I understood.

Hana was dying.

When I arrived at West End Central, a stocky Chinese man in his sixties was standing under the big blue lamp that marks the entrance to 27 Savile Row.

I recognised him as the man that Edie had been interviewing before we opened up the lorry, the man who had called it in. They must have taken him to the station for a longer interview and now they were done with him. He looked at me warily as I came up the steps.

‘Thank you for your help, sir,’ I said.

He shook his head.

‘I’m not sure I was very much help.’ He glanced back at the entrance to West End Central. ‘I told your colleagues everything I saw but I don’t think they believe me.’