After discovering the body of an undercover police officer in the trunk of a car, the CID team blunder into a Drugs Squad operation against a major trafficker that appears to implicate one of their closest colleagues.

Season 2 returns to Cambridge as Professor Jasper Tempest and the team untangle a series of knotty crimes ranging from an unexplained fire in a student block to the mystery of an entire family found dead in their home. The Professor also gets help of his own, as he embarks on therapy to unearth more secrets from his troubled childhood.