Amy and Eliza are held hostage by the dissidents at the heart of the investigation, who demand their help to infiltrate the base. Kirsten will do anything to find Amy.
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.