In the office at MI5 where he works, they call Jonas Merrick 'the eternal flame'. It isn't a compliment. It's because he never goes out. He never goes undercover, never does surveillance, never goes with the teams that kick down the doors or seize the suspects off the street. He commutes into work and sits at his desk and then he goes home. But Jonas has qualities the hot-shots fail to notice: a steely concentration, a ruthless ability to focus and find the enemy hiding in plain sight. Hearing of a British Jihadi returning from Syria with murderous plans, Jonas sends out for a telling photograph: a crocodile, almost submerged, just its eyes above water as it waits for unsuspecting prey to drink at the riverbank. Coming ashore near Dover, Cameron Jilkes is a young man from a broken home and a failed education, trained in the harshest theatre of war, driven to rage by loss and pain. And this time, 'the eternal flame' must go out - to hunt the crocodile himself.