Now retired to his family farm in his native Brittany, Peter Guillam – who narrates the story in the first person – is summoned to Circus headquarters to account for his actions during Operation Windfall, the espionage mission depicted in The Spy Who Came in from the Cold.

Tulip was then flown to England and taken to a covert farm run by Joint (due to its participation in her exfiltration), where she was promptly murdered by Stasi hitman Mundt, who was then captured after stepping into an ancient leg-hold trap on site while escaping.

The other agents at the safe house were told only that Tulip had killed herself, and that the unidentified person caught in the leg-hold trap worked for internal Circus security.

The only people who knew the truth were the handful from Covert who had been "read into" Operation Windfall, including Control, Smiley, Guillam, and Prideaux (who was the handoff contact for Mundt).

However, in the course of her defense, the lawyer covertly acquires secret reports compiled by Special Branch (apparently requested by Joint in an effort to identify the source of Operation Windfall), who had tailed Leamas after he was pensioned by The Circus.

Guillam then locates Prideaux, still at the same prep school as in Tinker Tailor Soldier Spy, who tells him to contact Smiley at a particular library at the University of Freiburg in Germany, near both the French and Swiss borders.

Smiley agrees to not only authorize the release of the covert records but to also provide a deposition about the events, noting to Guillam that everything he had done had been motivated by his vision of "leading Europe out of her darkness toward a new age of reason".

During the events of the book, updates are provided on several characters from earlier books: In an interview with the NPR series Fresh Air broadcast in the United States on 5 September 2017, le Carré told host Terry Gross that one of the reasons for writing the novel was "to make a case for Europe" in the wake of the 2016 British referendum, which resulted in a slim majority voting in favour of leaving the European Union.