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 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