1974, in the middle of the Cold War. The three-day week, petrol rationing and industrial strife has plunged Britain into a State of Emergency.

Against this turbulent backcloth Charles Thoroughgood, a trainee spy in MI6, Britain's Secret Service, is asked to revive his former friendship with Viktor Koslov, a Russian Diplomat he knew at University with a view to 'turning' him. But Viktor has his own agenda and reveals a shocking truth about Charles’ own family that threatens to derail him, both personally and professionally.

He is catapulted into a dangerous personal odyssey to uncover the truth but finds himself drawn into a lethal KGB plot to mount an attack within the UK.

His life is further complicated by a relationship with the wife of another agent. He is forced to realize that betrayal can take many forms.

Charles Thoroughgood is played by Charlie Cox, Viktor Koslov by Andrew Scott, Hookey by Simon Russell Beale, Anna by Romola Garai, Hugo March by Christian McKay, Eva by Olivia Grant, Joyce by Tessa Peake-Jones and Martha by Geraldine James. (Source: BBC Media Centre)