Now elderly and living in retirement on a farm in his native Brittany, Peter Guillam – who narrates the story in the first person – is summoned to MI6 headquarters to account for his actions during Operation Windfall, the espionage mission depicted in The Spy Who Came in from the Cold. Learning that Leamas' now adult son, Christoph is suing the British government for wrongful death, Guillam ruminates on the course of events that led to the death of agent Karl Riemick, and how Guillam and Leamas desperately worked together to try and save not only Riemeck's life but the lives of several other German citizens working with him to provide intelligence information to Britain.

The book alternates between Guillam's recollections of the events leading up to Leamas' demise and his attempts in the present day to eschew guilt for his role; his avoidance of Christoph, who wants to extort him; and his efforts to learn the whereabouts of Smiley, who has gone off the grid following his own retirement.