‘Seven days now.’ I talked him through the mall swap, the email she’d sent from the IT café. Stefan checked the locations on a map, then sat back and sipped his Red Bull. It was a relief to have someone I trusted around. Stefan had been a teenager when I first met him, ten years ago. He came to my attention in a dusty office belonging to New Scotland Yard’s cyber crimes division. Seventeen years old, born in north London to Polish parents, he’d been arrested for hacking his school’s system, promptly hacked into the police unit investigating him, then crashed the Home Office website. He already had a criminal record for breaking into electronics stores. He’d tried to escape the country but was picked up at Dover with his brother’s passport. I got him released the next day. A year later he was helping GCHQ develop battlefield capability, and a year after that directing cyber ops in Afghanistan. If he ever wished I’d left him on the run, he was polite enough not to say so.

A couple of years later I was in Dubai when I heard that someone at the Burj Al Arab was wiping minibar accounts from the hotel system. I found him locked in his room, war-fatigued, drinking a cocktail of Mountain Dew, tequila and Zopiclone, and gambling heavily. I paid off his debts and put him in touch with Marius in Romania, who regularly asked for contacts on the ground: people who could infiltrate delivery chains or break into places covertly. Stefan was trained in all that. He had the rare combination of skill and greed that made men return to conflict zones voluntarily. I got him a six-figure salary, knowing he was worth twice as much.

‘You think she’s still in the area?’ he asked.

‘I think it’s a possibility. I think she discovered something that was dangerous for her. Look out for the words “Perfect Vision”,’ I said. ‘And “Catalyst”.’

Stefan nodded. He’d heard enough cryptonyms in his time, and knew not to ask for more knowledge than he needed. The more you knew, the more people wanted to torture you.

I showed him the map I’d marked up with cafés and restaurants near the buildings I was interested in, anywhere targets might gather. Often the secret was not to try and directly hack the offices themselves, but find where staff congregate with unprotected smartphones and laptops. Stefan had a Polar Breeze – a remote data-sucking device for tapping wirelessly into nearby computers – and a Stingray, which was able to mimic a cell tower and force all phones in a 200-metre radius to connect to it. From there, it could extract contact information, dialled numbers, text messages, calendar entries. It could give you a stepping stone into an entire network.