Season 1 ends with the team reeling from a KGB bombing and the mole's confession. With Operation Glass hurtling towards a shocking climax, MI5 tries to piece the puzzle together and avert disaster before it is too late.
The team reel from the shocking discovery of a mole among them. Meanwhile, the Soviet plot continues unabated, but Wendy tries to give the team the break they need; and Alan is forced to make a decision when Sarah is placed in danger.
British spies in 1972 London attempt to stop a secret Soviet plot to destroy Britain. In the opener, a defecting KGB officer reveals the plot to a MI5 agent, which leads to a secret team being created to investigate the threat.