‘This is what I’ve found,’ she said. ‘It is the same voice on both the Mahmud Irani and the Hector Welles tape. The voice has the glottal stops of a London or southeast England accent, but there are distinct signs of modification – think of it as an Estuary accent that has learned Received Pronunciation. In other words, the subject is not speaking with the voice that he grew up with. Either he has had elocution lessons or, more likely, moved to a social strata beyond the environment of his parents. It happens a lot. For most people, a university education will do it.’

And I thought about her own voice.

There was nothing wrong with it. But now I knew of her deafness it was as if she was saying the words but not hearing them.

‘And there’s something else,’ she said. ‘There is an unusual cadence to some of his sentences, as if there was a foreign language spoken in his home. And he can speak it too.’

I was impressed.

‘And you know all that from one sentence?’ I said.

I smiled at her.

She didn’t smile back.

‘Voice biometrics – the digital analysis of speech patterns – is all done by software,’ Tara Jones said. She gave me a cool look. ‘So I think you’ll find that my deafness is no impediment to my job.’

‘Of course not,’ I said, my face flushing with shame.

The door to MIR-1 opened and DCI Whitestone walked in. She seemed ten years older and ten pounds thinner than when I had seen her last night. She looked shattered. She stared at us and we stared back.

The silence was broken by Billy Greene.

‘Jesus Christ,’ he said. ‘We’ve got another one!’

Then it was on the big screen.

A young man with tightly cropped hair was being led into that room where the sun did not reach, as the dark figures hovered in the background pinning something to the white brickwork stained green with the ages.

‘There’s no time-and-date stamp,’ Edie said.

I turned to Colin Cho.

‘Is this live?’ I said.

He shook his head. ‘I don’t know, Max.’

‘Is it live?’ I shouted.

‘I don’t fucking know, Max!’ Colin shouted back. ‘Give us a chance!’

The PCeU team desperately huddled around a single laptop. The phones all began to ring at once because they were about to reach the magic number. Three is the magic number.

The Hanging Club were about to become serial killers.

I looked at DCI Whitestone for guidance. But she had slumped down into a workstation as if she was tired beyond belief, as if she had not slept for days.

And her eyes never left the big screen.

‘Marble Arch, Edie,’ I said. ‘Go with her, Billy. I’ll call CTC and get some bodies down there in case they’re dumb enough to dump the body in the same place.’