The next agent on the Soviet list, Tom Mallory, is a brutal man currently in prison for assault. Without his freedom, he can't perform his task and bring MI5 one-step closer to thwarting Operation Glass - leaving Daddy with a terrible choice. Joe, haunted by events in his past, continues to struggle with his lover's killer's role in the plot.

Discovering the KGB is one-step ahead, Joe tries to convince the team to run a double agent scheme - a perilous game that understandably makes his colleagues uneasy. But with dangerous assassin Odin at large, the team is unsure KGB defector, Arkady, would risk his life to help them. Meanwhile, Alan grapples with a shocking discovery that could jeopardize his marriage to fellow agent and wife, Sarah.