‘Go now.’ She woke from the mental paralysis, grabbed Maryam’s hand and plunged down towards the ticket barrier, towards the safety of the tunnels far below her feet.

#

CTOC, St Pancras, London

In the CT ops room, Gabriel was sat at the conference table coming to the end of an update when a flustered DS came over.

‘Ma’am. There’s been an incident.’

Gabriel swivelled towards the SO15 video screens. A helicopter camera showed a street close to Trafalgar Square where dots of churning protesters were crushed together. In the midst of the crowd was a gap, maybe fifty metres across. At its centre were four or five plumes of black smoke.

‘What the hell’s that?’ said Gabriel. ‘Flares?’

‘Gold Command report petrol bombs, ma’am. Presumably thrown by one of the marchers.’

‘What do you mean “presumably”? Are you telling me that someone on that march got out and lit a petrol bomb without being spotted?’

‘That’s all I’ve got, ma’am,’ said the DS uncomfortably.

The camera zoomed to the source of the smoke – patches of orange flames flickering up from the road. Even from the height of the camera, it was clear the crowd was panicking. Gabriel could see people sprinting from the fire. What idiot would do that on a demo? Anarchists maybe? Unlikely to be terrorists, surely. But with kids around? She imagined the scene in Gold Command right now. It would be calm over there but bloody busy. They’d have to let the crowds disperse and they would be deploying armed teams. But until she heard otherwise, it was their concern, not hers. She waited.

‘Ma’am.’ It was the DS again. ‘Reports of gunfire in the same street. Armed response units are moving in to the source.’

Gabriel looked again at the screen with new eyes. Everything was immediately different. If guns were being used, then this was unquestionably a terror attack. The NRF? An Islamist group? Was this two of three?

She stood up. Speculation later, action now. ‘Get a CT team down there now – and get SOCOs,’ said Gabriel to the team around her. ‘First priority is finding the source of the attack – in the crowd, or an overlooking building. My guess would be the latter. Secure the crime scene once casualties are out. And get me photos.’

The flames had burnt themselves out, but the road surface was smouldering. The road was littered with white placards and abandoned banners. Some were scorched.

‘What’s that?’ said Gabriel. ‘Can’t they zoom in there?’

She pointed to what looked like a discarded blanket lying in the road. The object moved and a police officer ran over and crouched next to it. It was only then that Gabriel realised it wasn’t a discarded blanket at all, but a body.

‘Getting reports of seven, no, eight people down now,’ said the DS. ‘Two more – it’s carnage, ma’am.’

#

Pall Mall, London

Rod Houghton and Dougie Glenister, dressed in dark grey hoodies and jeans, emerged from room 312 of the A-Line hotel. They checked the corridor was clear, then the shorter man opened the door and went back into their room. After two seconds, he emerged and shut the door, sending a waft of black smoke curling into the corridor.