DI Perez investigates the disappearance of a vulnerable young man, whose family are new to Shetland.

After the discovery of an unknown body, the search for Connor grows increasingly desperate. Perez follows Danny on a perilous journey into his murky past.

Mounting evidence pushes Perez and the team to revise their view of Connor Cairns. Is he a vulnerable missing person or a killer on the run?

Perez issues a warrant for Connor's arrest and looks for the motive behind his bomb-making. Sandy tries to find out what business William Rodgers had in Shetland.

Perez tries to get the measure of Lloyd. Evidence emerges of another bombmaker. The net closes in around Martin. Sandy uncovers Connor's interest in a piece of local history.

The team races to identify the killer and prevent disaster striking Lerwick. As the investigation draws to a close, Perez faces a life-changing decision.