She had met Tennant in person by then, and she had liked him, so she took the decision to contact Tennant, unofficially and discreetly, to warn him that his PA was leaking. Looking back now, it was a foolhardy move that could have ended her career. But at the time, she had simply done what she felt right and fair.

The media campaign did not end, but it calmed down and it had been two or three years since the Herald had run a PC PC story. Perhaps they had simply got bored. And the deputy commissioner had himself been forced to resign a year earlier over a tasteless joke about a strip club.

Tennant continued: ‘And it’s not just the press, Sophie. I had the Deputy PM screaming down the phone earlier.’

‘I take it she’s not so keen on the current demonstration of free speech outside her kitchen window,’ said Gabriel.

‘Between you and me, I despair with this current generation of politicians. We’ve got the rise of the extreme-right terrorism, the continued threat from Islamists, and we’re in the middle, supposedly protecting the public. And meanwhile, the political class on every side seems more interested in chucking fuel on the fire. Not just Hogarth and her friends; the Shadow Home Secretary’s almost as bad, chumming up to Sherif and his cronies.’

Tennant had never been so indiscreet in front of Gabriel before. She was flattered, but also alarmed at the depth of his bitterness. She tried to laugh it off. ‘It’s technically what they called at Police College a shitstorm, sir.’

‘Indeed.’

Gabriel could hear from his voice that he was smiling. ‘Listen, boss, there’s another reason I’ve rung.’

She filled him in on the video filename. ‘You know how obsessed these people are with codes. I’ve been puzzling over part of the name. A underscore C. I think it’s a number code – one underscore three. And I think I know what it means. One out of three. I think the NRF planned Chilton Park as the first in three attacks, coming in quick succession, to announce their arrival on the scene.’

‘That’s a hell of a leap from two letters on a video filename, Sophie,’ he said. Gabriel felt the kick of disappointment.

‘Not just the filename, boss. The language. The tone. The way that it mimics a suicide video. We thought this wasn’t a one-off yesterday – well, this is the proof.’

‘Why underscore? Why not one slash three?’

‘Computers can’t cope with filenames containing slashes, I’m told. But it’s not just the name. It’s part of a bigger jigsaw. And it means we must widen the scope of the investigation – it’s not just about tracking down Fletcher, it’s about cracking open the NRF and preventing two more massacres.’

Tennant sighed. ‘I don’t think it’s enough, I’m sorry. I’ll talk to the head of Thames, but I’m not convinced she’ll share your interpretation. I’m not sure I do.’

#

At New Scotland Yard, Tennant ended the call. Time to go home? Time to appease Chris with an appearance before 10pm? Tennant was gathering his stuff when an email popped up on his screen from the head of operations upstairs. Tennant read it with a sinking heart.