When an officer is cuddled on base, Eliza warns Amy to get control of her investigation. Meanwhile, Kirsten uncovers key evidence linking a squadron member to the attack.
The mysterious disappearance of a Scottish fishing trawler and a passing on-board a Trident nuclear submarine bring the police into conflict with the Navy and British security services. DCI Amy Silva leads an investigation on land and at sea into a conspiracy that threatens the very heart of Britain's nuclear deterrent.