Two months following the death of Lucas North, and 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. With help from Home Secretary William Towers (Simon Russell Beale), Harry returns to work on a provisional basis until the tribunal's conclusion. Harry learns that old friend Max Witt (Giles Havergal) was murdered. His Russian opposite, Ilya Gavrik (Jonathan Hyde), is smuggled into the country by Towers, who reveals Gavrik is proposing a partnership between Russia and the United Kingdom without the Americans knowing. It has emerged that Witt was killed 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. Section D learns of a kill order by the Chechens on Gavrik during a function. Harry intercepts the assassin, who flees and then killed by new Section D Chief Erin Watts (Lara Pulver). Despite this, the assassin's handlers deem the mission a success. Harry meets with Elena, and tells her they should meet again at a safe location. Later, Harry reveals to Ruth that he and Elena were lovers, and that FSB officer Sasha Gavrik (Tom Weston-Jones) is their son.
