|Series 10, Episode 01|
|Air Date||18 September 2011|
|Previous||Series 9, Episode 8|
|Next||Series 10, Episode 2|
Two months after trading Albany, a state secret, for Ruth Evershed (Nicola Walker), Sir Harry Pearce (Peter Firth) is on garden leave until a tribunal can determine his future with MI5, however Home Secretary William Towers (Simon Russell Beale) arranges for Harry to return on a provisional basis until its conclusion.
Harry learns that Towers has smuggled his Russian opposite, Ilya Gavrik (Jonathan Hyde), into the country to propose a strategic partnership between Russia and the United Kingdom without the knowledge of the United States government. It has also emerged that a friend of Harry's, Max Witt, was murdered because he knew somebody is posing as Harry using his old coded messages from the Cold War; the imposter made contact with Elena (Alice Krige), Gavrik's wife, and Harry's former asset.
After Section D learns of an assassination plot against Gavrik during a function, new Section D Chief Erin Watts (Lara Pulver) manages to stop and kill the assassin. Despite this, the assassin's handlers deem the mission a success. Later, Harry reveals to Ruth that he and Elena were lovers, and that FSB officer Sasha Gavrik (Tom Weston-Jones) is their son.