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.
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.