London: 1972. When a defecting KGB officer, Arkady Malinov, reveals Operation Glass, a devastating Soviet plot that could change the course of the cold war, Daddy, the head of MI5, assembles a secret team to investigate. As the Soviets awaken a list of sleeper agents all over Britain, Daddy's team must move swiftly to gain information about the plot.

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.

The team discovers a sleeper agent with terrifying connections in the US military. Faced with a formidable foe who not only appears to be a traitor, but a trained spy with access to US bases, MI5 may be out of its league. Meanwhile, Daddy is on a mission of his own to secure the safe defection of his favourite Chinese dancer.