In the summer of 1958, an inventor is tasked with a mission by MI5. Following the Soviets' launch of the first intercontinental ballistic missile, fear permeates the lives of all.

Hannah arrives at Buckingham Palace, but is too late to be presented. Samuel meets two men from MI5 who are interested in his invention and he is sworn to secrecy.

Samuel does not want the business of Mr Field and Denning if it means being blackmailed - but Courtney reveals the company is close to bankruptcy and must acquire more orders. Clutching at straws, Kathleen visits Sacha's school to see if she can glean any clues about her son Anthony's disappearance.

Kathleen visits the boarding house in search of Anthony, but has no luck. Armstrong explains to Samuel that they have reason to believe that people connected with the Shaw family could be enemies of the state. Not knowing who to believe, Samuel confronts Mr Field.

After the shooting, Field places the Petruhkin home and factory under protection. Samuel makes his own plans and goes into hiding where he meets Kathleen in secret.

Samuel learns the truth about the Shaws and the MI5 men. His is invited to an extraordinary secret meeting, while Hannah becomes increasingly worried about her father's safety.