Amy is trapped and running out of time, but will assistance arrive too late? On land, Kirsten chases down the traitor's accomplice. When the traitor on Vigil puts their plans into action, the crew are forced to fight for their lives.
The mysterious disappearance of a Scottish fishing trawler and a death 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.