DI Ruth Hunter and DS Nick Evans witness a horrifying collision in Snowdonia. A teenage boy sprints into the road: what was he running from? Callum Roper doesn't survive the crash. In his possession were prescriptions for painkillers and tranquilisers, not in his name.

He had severe scars on his palms and abdomen, a tattoo reading 'Thomas' and a recent rifle-shot wound. This isn't just a drug-running case. Across the fields from the site of the collision is a farm housing The Family a cult led by Rachel who believes herself a true prophet, sent to save the souls of her flock even when they resist.

With a missing person's report also linked to The Family, the investigating team are given 72 hours of surveillance. 72 hours that will change everything...