That was the nature of the relationship between SO15 and MI5. In the early days of a case, Thames led the joint operation, supported by police. If arrests were needed, or an attack was looming, Thames handed the lead to the police but continued their support.

‘MI5 are calling this investigation Operation Hippocampus,’ said Gabriel. ‘Terrible name, but there you go. You’ve done some amazing work over the last few years on returners, so I want you to focus full-time on Abu Mujahid – be our liaison with MI5. Liaise with Thames and get some feelers out via the CTPLO network.’

Counter Terrorism Police Liaison Officers were the Met’s global eyes and ears. There were currently forty-eight experienced counter terrorism detectives working in partner nations and source countries, usually based in British embassies and often operating closely with MI6 officers.

‘And we need more on the Global Islamic Defence,’ Gabriel continued. ‘If the intel from Rachel Isaacs is reliable, there’s a strong chance Abu Mujahid is involved in whatever the GID are planning. We know there is an arms and explosives shipment coming from Greece and it’s safe to assume it’s heading to him.’ Bose left Gabriel alone in the conference room. She opened up the Abu Mujahid file and began to flick through it once more.

She struggled to focus. Her mind kept drifting back to the supermarket CCTV. There was something obscene about the image of Abu Mujahid wandering through the aisles of baked beans and spaghetti, as if he was just another ordinary shopper. It was like opening a fridge door and coming face to face with an alligator. Focus, woman, she told herself, and read again.

Born Jack Stephen Pearce, in Haringey. Aged twenty-seven. Parents divorced aged five – father in sales, mostly absent, mother died six years ago. One older brother in the north, selling cars. Brother isn’t close to his family, thought Gabriel, but should be watched.

Bright, ruthless, geeky. Grade A student until fifteen, then he went off the rails. Predictably, got into dealing – coke, LSD, methadone. Aged eighteen, he was stealing pushbikes and mopeds. Picked up by police aged nineteen, convicted and given a suspended sentence and community service. A year later, he was picked up again. This time he got two years in Wandsworth.

Until then, Jack Pearce had shown no interest in religion. But in prison, everything changed. He fell in with Ishmail Sherif, then an up-and-coming preacher doing time for fraud, and within six months Jack Pearce had converted to Islam. By the time he left prison, he had a mission and new friends.

On the outside, Pearce worked at the North London Mosque for a few months as a volunteer. Once off licence, and free to travel, he went to Pakistan for four months. And there he got intensive training in explosives, basic terrorism craft and handling weapons, along with some impressive leadership training. He left Britain an awkward twenty-two-year-old, and returned eight months later a charming, charismatic manipulator. God knows how they did it, but it was an extraordinary transformation, according to those who knew him.