The second is to take the door on your right and climb up the staircase where you have to open a door using 9 Technical ability. You get the feeling, from the way James begrudgingly warmed to the drama as it ran its course (“Anything can improve,” he wrote, “even Tinker, Tailor, Soldier, Spy, of which the latest episode was a good deal less wearisome than the previous three”), that some of the invective was for effect. After Control's death, Esterhase embraces the new Alleline regime and allows his Lamplighters to be almost entirely given over to serving Operation Witchcraft, which is in fact nothing but a disinformation campaign orchestrated by Soviet spymaster Karla. Alleline obtained ministerial support to circumvent Control's authority, and his post-Testify promotion supporters Haydon, Esterhase, and Bland have sponsored it.

According to one legend, at "Yelnya", Karla caused the Germans to shell their own forward line (presumably a reference to either the Yelnya Offensive during the first Battle of Smolensk, or the second Battle of Smolensk). It has been adapted into both a television series and a film, and remains a staple of the spy fiction genre. Smiley explains his belief that somewhere in the gap between these two conflicts, Karla travelled to England and recruited Gerald. In 1980, le Carré defined Smiley's politics as: "I think he stands where I stand; heTarr defends himself by explaining that he was informed of a Soviet mole at the highest level of the Circus – codenamed Gerald – by Irina, the wife of a trade delegate, while in Hong Kong. It is set in London in the early 1970s and follows the hunt for a Soviet double agent at the top of the British secret service. Several real-life intelligence figures have been postulated as models for Karla, including KGB General Rem Krassilnikov, whose obituary in the New York Times stated that his CIA opponents viewed him as a real-life Karla. During the events of Tinker, Tailor, Soldier, Spy, Esterhase has a son at Westminster and a daughter at medical school.

Metacritic, which assigns a normalised rating in the 0–100 range based on reviews from top mainstream critics, calculated an average score of 85 based on 42 reviews, indicating "universal acclaim". The final song in the film, Julio Iglesias' rendition of the French song " La Mer", set against a visual montage of various characters and subplots being resolved as Smiley strides into Circus headquarters to assume command, was chosen because it was something the team thought George Smiley would listen to when he was alone; Alfredson described the song as "everything that the world of MI6 isn't". Stateside, Peter Travers of Rolling Stone wrote, "As Alfredson directs the expert script by Peter Straughan and Bridget O'Connor, the film emerges as a tale of loneliness and desperation among men who can never disclose their secret hearts, even to themselves. Writing in The Atlantic, le Carré admirer James Parker favourably contrasted Smiley with the James Bond franchise but found this Tinker Tailor adaptation "problematic" compared with the 1979 BBC mini-series.

Smiley is also given access to Circus documents, and begins by examining Alleline's restructuring, discovering the ousting of Jerry Westerby and Connie Sachs, as well as slush fund payments to Jim Prideaux.

Smiley offered Karla his lighter, a present from Ann, to light a cigarette, but Karla rose and left with it.The secret service seeks to dispense with that humanity, the consensus on high being that humane virtues have outlasted whatever limited usefulness they might have had.