‘John Mardell.’ Hawkins got straight to business, sensing that pleasantries were a waste of everyone’s time. She retrieved a mugshot of the watcher from her bag. ‘I arrested him yesterday afternoon. He’s now in custody, but won’t even confirm his name. The only reason we have an ID is because his prints came up on your system, except the information appears to be classified.’

Whiting took the photograph. ‘That’s Mardell, all right. I looked him up after we spoke on the phone.’ He reached for the laptop on his desk, tapped a few keys before rotating it so Hawkins could see the file on screen, all text apart from Mardell’s name censored. The same face stared back at her.

She nodded. ‘What did he do to earn such notoriety?’

‘I’ll tell you what I can.’ Her host inhaled, clearly composing his answer. ‘John Mardell, forty-seven, last known to be living in Islington. Had a couple of custodial sentences in his twenties for random violence, then a longer one for a more serious offence in ninety-eight, when he almost killed another man in a bar fight.’

‘Do we know what they were fighting about?’

‘I’m afraid not.’

‘And since then?’

‘Oddly, that incident was the last of its type. Perhaps the experience changed his behaviour.’

Her lips pursed. ‘Or he got better at hiding it.’

‘Either way, he hasn’t been convicted of a thing since.’

‘Interesting. But none of that would draw attention from SO15. Surely there’s more.’

‘Very perceptive.’ Whiting nodded approvingly. ‘Mr Mardell has been on our watch list for almost two years, not for anything he’s done directly; more by association. He’s believed to be a minor but long-standing member of a group known as Millennial Dawn, a spiritualist organization that denies the right of similar groups to exist. There’s disagreement about how actively they follow such doctrine, but they demonstrate several practices typical of terrorist sleeper cells. Some of our team believe they were responsible for a nail bomb that could have maimed hundreds of worshippers near Stonehenge in 2013, had the bag not been left in long grass, to be saturated by heavy rain that knocked out some of its wiring.’

Hawkins felt a cold trickle of plausibility lift the fine hairs on her neck. ‘What else do you know about them?’