Police investigations collide with the security services and armed forces in this atmospheric mystery from the makers of `Line of Duty'. In the first season, a trawler's inexplicable disappearance leads investigators below the waves into a world of intrigue. In the second, a series of military base murders leads to even more shadowy discoveries. Suranne Jones, Rose Leslie and Gary Lewis star as the police investigators fighting to continue their work against claims that they are out of their depth.