On his return from Pakistan, he was stopped and interviewed at the border. Nothing could be proven, but Pearce had the attention of MI5. He was rated initially as a high threat on the ladder of risk used by Thames and SO15. There were some four and a half thousand suspects of interest at the time he came back from Pakistan and within four months of his return to the UK he was in the top thirty.

Within six months, he had a cell preparing for an attack on a music festival in Cornwall using spiked drugs. An uneasy part of his drugs supply chain tipped off police and he was arrested. He went on trial for conspiracy to commit murder with two associates, but while they went down, Jack Pearce was cleared on a technicality.

And then Gabriel got involved. The facts of that next year were engraved on her head. She hadn’t needed to review them last night. The Home Secretary put a control order on him. And then, after Gabriel diverted a surveillance team to a live emergency, he slipped away, killing Isobel Harris as he fled the country.

In Syria, he popped up five months later, working his way up the ISIS hierarchy, under his kunya, Abu Mujahid al-Britani. He was implicated in the beheadings of two Canadian aid workers, and the massacre of twenty-five government supporters. He rounded them up from their cell, crammed them into a cage and set fire to them. Two were children.

He took part in an attack on a Druze community in Jabal al-Druze which left ten dead, and was suspected to have been part of a beheading of a US journalist. His last sighting was in Aleppo three months ago. And then he went off the radar.

And I let him go. Those deaths – Isobel, the Canadians, the children, they are on my head.

The thought was there before Gabriel could put it back inside the box where it belonged. She knew with the rational part of her head that it was nonsense. She knew she had been cleared. That the choice she had made that had led to Abu Mujahid slipping away had been a reasonable one. In fact, it had been the best one available to her. But it wasn’t the right one. How could it have been? And the other voice, the one that spoke to her from her guts, told her she was to blame. She had failed those anonymous victims in Syria. She had failed Isobel Harris, and her parents. She’d failed her own dad. And, Jesus, it was coming back to haunt her.

And she had been right. That was the galling thing. For the last seven days, she had known he was back in the UK – and for seven days, she had taken her eye off the ball. No, she corrected herself, she had been forced to take her eye off the ball. What damage had that week done? How far behind were they, when they could have been snapping at his heels?