It was early evening and we were standing at our workstations, ignoring the phones that were ringing all over MIR-1, as the man was helped onto the kitchen step stool and a noose was slipped round his neck.

And the terrible exchange between the two men.

‘Do you know why you have been brought to this place of execution?’

‘What? This – what? I don’t understand. What? I’m a taxi driver—’

The voice of the first man muffled by some sort of mask. The voice of the second man choked with terror.

‘Who is he?’ DCI Pat Whitestone said.

‘IC4,’ said DC Edie Wren, running a hand through her red hair, her eyes not leaving the giant screen. IC4 meant the man – the one we could see, the one with the noose around his neck – was of South Asian descent. ‘Maybe forty years old. Unshaven. Jeans. Polo shirt. Lacoste.’

‘A Lacoste knock-off,’ I said. ‘The little crocodile’s looking in the wrong direction.’

‘Where is that place, Max?’ said Whitestone.

I took a few steps closer to the screen. The film was sharp but the room was dark. In the shadows I could glimpse white tiles or bricks, stained green and yellow by time and the weather.

I felt I had seen it before. It was some part of London that was just round the corner, and yet a hundred years away, and beyond the reach of memory. I took a step back.

‘I don’t know,’ I said.

‘What are they doing to him?’ said Trainee Detective Constable Billy Greene.

Then the stool was kicked away and we did not speak as we watched the man hang, his body twisting and squirming in the air, and there was no sound but the strangled gurgling coming from his throat. When the hanging man began to soil himself the cameraman turned away and I caught glimpses – nothing more – of two or three figures in dark clothes, their faces covered in black masks, only their eyes showing, their backs pressed against those yellowing walls.

‘There’s three or four of them,’ I said. ‘Maybe more. Wearing ski masks. No, not ski masks – they’re tactical Nomex face masks, or something similar.’ A pause. ‘They know what they’re doing.’

The man’s face began to change colour as the life was strangled out of him. Then he was still and it ended. A film lasting ten minutes and twenty-one seconds that was suddenly trending all over the world.

‘You seen this hashtag?’ Edie said, hunched over her laptop. ‘It’s everywhere: #bringitback.’

‘Bring what back?’ said TDC Greene.

‘Play it again,’ said Whitestone. ‘Answer the phones, Billy. Find out where the hashtag comes from, Edie.’

Edie began tapping on her keyboard.

‘Does that look like a hate crime to you, Max?’ Whitestone said.

‘It looks like a lynching,’ I said. ‘So – yes, maybe.’

‘Here,’ Edie said, and then a panel appeared in a corner of the big screen.