When a prominent and controversial Shetlander is shot dead on their doorstep in broad daylight, Perez rushes back from his mother’s funeral to lead the investigation.

As Perez closes in on the identity of Galbraith’s killer, he struggles with Duncan’s secret, while Donna has one more surprise in store.

After the shocking events of the previous night, Perez must piece together what happened before a rampaging and vengeful Creggan finds his target.

Facing a dead end in the hunt for Galbraith’s killer, Tosh leads Perez to the remote island of Fetlar. Donna asks Duncan for one last favour.

In the aftermath of the diving incident, the team searches for a link between the two bodies. Meanwhile, Perez must deal with the return of Donna Killick.

The hunt is on for Sandy's attacker, before a shocking confession causes tensions to boil over and some Islanders take justice into their own hands.