ESUS is an experimental unit set up to try and forge closer links between MI5 and the police force. The unit is headed by MI5 agents, but the rest of the team have been seconded from regional police forces because of their specialist undercover expertise. ESUS brief is to investigate cases that go beyond the rimit of either the regional police forces or special branch after ESUS. When junior Parlimentary Under Secretary Peter Gleeson commits suicide after being exposed as a homosexual in Exclusive! magazine the team go undercover to investigate a private drinking club called The Golden Goose where they become embroiled in scandal, blackmail and tragedy.