Taverner is desperate to hide dangerous secrets. River seeks answers at his grandfather’s house.

When an officer is stabbed on base, Eliza warns Amy to get control of her investigation. Meanwhile, Kirsten uncovers key evidence linking a squadron member to the attack.

Amy and Eliza are held hostage by the dissidents at the heart of the investigation, who demand their help to infiltrate the base. Kirsten will do anything to find Amy.

The Syrian foreign minister tries to establish subversive contacts with MI5 at the opening of a cultural centre in London. Fiona is desperate to lead this mission and must confront…