I nodded. Professor Hitchens still wasn’t looking at me.

‘Tyburn,’ I said. ‘We found the first victim on the Park Lane side of Hyde Park. Not far from the site of Tyburn.’

He looked at me at last.

‘Where this country hanged people for a thousand years,’ I said.

Professor Hitchens grinned at me, though there was no warmth in his smile. His chipped teeth also looked old beyond their years. I wasn’t crazy about him, to tell you the truth.

‘I know what Tyburn was, Detective Wood.’

‘Wolfe.’

‘Detective Wolfe,’ he said, and he turned in his swivel chair to address the room at large. Fat yellow fingers tapped the armrests of his chair. ‘But Tyburn was most emphatically not in Hyde Park.’

‘No, I know that, but—’

‘The location was further north – according to the Rocque map of London in 1746. Are you familiar with Rocque’s map of 1746?’

I briefly shook my head to confirm I was not familiar with Rocque’s map of eighteenth-century London.

‘The actual location of the Tyburn Tree was on the traffic island where the Edgware Road, Oxford Street and Bayswater Road all meet,’ Hitchens said.

‘But they’re not going to dump a body in the middle of a traffic island, are they?’ I said, and watched him bristle, unused to being contradicted. I suppose these big-shot academics get used to students hanging on their every word. ‘What about that kitchen step stool, Professor?’ I said. ‘That look late Victorian to you?’

Whitestone shouted across the room to Wren. ‘Still no ID of the vic, Edie?’

Wren shook her head. ‘Colin’s monitoring the online traffic and Billy’s got an open line to Metcall, but nothing yet.’

Metcall, also known as Central Communications Command, is responsible for public contact. If someone hit 999 because they knew the man who had just been hanged online, it would come through to them first.

‘Play it one more time,’ the Chief Super said.

TDC Greene hit the button and we watched in silence as the scene unfolded again. Somehow repeated viewing had not drained the hanging of its power to shock.

The man in the suit and tie fighting for his life. The desperate struggle before he was dragged onto the stool they used for a makeshift scaffold. The last words he would ever hear: ‘Do you know why you’ve been brought to this place of execution?’ His strangulation on the end of a rope. His hands unbound, tearing at his throat.

And the boy. The picture on the wall of the smiling young boy, who smiled just as sweetly and innocently as the girls had smiled when Mahmud Irani died. Smiling from beyond the grave, smiling for all eternity.

‘What the hell are they doing, Dr Joe?’ Whitestone said quietly to our psychologist.