During the tumultuous summer of 1958, Samuel prepares to launch his new invention, which is attracting some suspicious followers, before meeting the mysterious Kathleen.

Hannah arrives at Buckingham Palace, but is too late to be presented; the secret service tasks Samuel with spying on the Shaws, in exchange for an order of his invention; Hannah discovers that Kathleen has a tragic family secret.

Samuel spies on his new friends while his relationship with Kathleen intensifies. He is tasked by Mr Field to find out the names of those attending the Shaw's party. After the party, Mr Field and Denning are unhappy with Samuel's lack of detail.

Kathleen has a new lead on Anthony; Sasha does his own investigating at school, which has dramatic consequences; Lord Wallington reveals more about the MI5 men to Samuel.

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, and is invited to an extraordinary secret meeting; Hannah becomes increasingly worried about her father's safety.