The mysterious disappearance of a Scottish fishing trawler and a death onboard a Trident nuclear submarine bring the police into conflict with the Navy and British security services.
Cast: Suranne Jones, Rose Leslie, Adam James, Lolita Chakrabarti, Lorne MacFadyen, Orla Russell, Tom Gill, Cal MacAninch, Aisha Toussaint, Reuben Joseph, Lauren Lyle, Anita Vettesse, Shaun Evans, Paterson Joseph, Gary Lewis, Anjli Mohindra, Connor Swindells, Martin Compston
Kirsten closes in on the killer, but their capture reveals the grave threat that Vigil faces. On the submarine, Amy makes a terrifying discovery.
Kirsten's investigation takes her into the heart of Scottish politics, but when she unearths a navy cover-up, it leaves Amy questioning who she can trust on Vigil.
With Vigil in danger, Amy must fight to continue her investigation. Meanwhile, Kirsten's enquiries lead to tragedy.
When a crew member is found dead aboard the Trident nuclear submarine HMS Vigil, DCI Amy Silva is flown out to investigate.