Newly-promoted to the murder team, Detective Jo Marshall investigates a perplexing double murder while working in secret.

As Jo and Sam struggle to find a link between Xav Palmer and Todd Drake, the discovery of the murder weapon shifts attention to the prominent landowning Benson family.

When Jo discovers that the two dead men and an accomplice targeted a nearby chemical company, she must find this third person before it's too late.

Jo and Sam find themselves with two surprising suspects in custody while the pressure mounts on Sergeant Mackie when he makes a discovery that turns everything on its head.

Donna makes some interesting admissions whilst being questioned, Sergeant Mackie's acts become apparent and Jo takes matters into her own hands.

Declan is located and Sergeant Mackie catches up with Jo.