A defecting KGB officer reveals a devastating Soviet plot; Daddy assembles an investigation team; Joe becomes obsessed with the reappearance of his nemesis.

A prisoner must be freed so he can aid MI5 with their campaign; Daddy has a choice to make; Joe struggles with his personal issues, but makes a deadly decision.

The team discovers a sleeper agent with connections to the U.S. military; Daddy wants to secure the safe defection of a Chinese dancer; Bobby tries to gain information on Daddy's life.

Joe tries to convince the team to run a double scheme; the team wonders if Arkady will risk his life for them; Alan struggles with a discovery that could jeopardize his marriage; Bobby's world unravels.

The team reels over the news about the mole; the Soviet plot continues; Wendy gives the team a much-needed break; Alan makes a tough decision when Sarah is in danger; leaked information threatens the investigation.

The team is bewildered over the mole's confession and a KGB bombing; MI5 is running out of time to stop the plot; Bobby and Wendy make a discovery.