Dan 'Spider' Shepherd's career path - soldier, cop, MI5 officer - has always put a strain on his family. So he is far from happy to learn that MI5 is using teenagers as informants. Parents are being kept in the dark and Shepherd fears that the children are being exploited. As an undercover specialist, Shepherd is tasked with protecting a 15-year-old schoolboy who is being used to gather evidence against violent drug dealers and a right-wing terrorist group. But when the boy's life is threatened, Shepherd has no choice but to step in and take the heat. And while Shepherd's problems mount up on the job front, he has even greater problems closer to home. His son Liam has fallen foul of the Serbian Mafia and if Shepherd doesn't intervene, Liam will die.