Teenager Luke Mullen was last seen getting into a car with an older woman. No one can understand why he has disappeared. His father - a former police officer - knows all too well that the longer he is missing, the more likely he is to turn up dead.

Then Luke's parents receive an anonymous video. It shows their son, eyes wide with terror, as a man advances towards him holding a syringe.

DI Tom Thorne recognises a psychopath when he sees one.

And the scene on the tape chills him to the bone - he knows that a child's life hangs in the balance, and that every minute counts...