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.
When a weapons test turns deadly, with allies from the Middle East among the dead, all eyes are on DCI Amy Silva, who tries to ignore the politics to get to the truth.
After escaping from a gunman with her life, Amy follows a new lead to the Middle East. There, she learns someone on the airbase was complicit in the attack. Meanwhile, in Scotland, Kirsten hunts down Chapman's killer.
When an officer is stabbed on base, Eliza warns Amy to get control of her investigation. Meanwhile Kirsten uncovers key evidence linking a squadron member to the attack.