It introduces George Smiley, the most famous of le Carré's recurring characters, in a story about East German spies inside Great Britain.

Although Smiley is a devout husband, Ann is serially unfaithful, and begins an affair with a Cuban racing driver before leaving the country with him.

Unsure about the meeting's purpose, he travels in via taxi to learn that Foreign Office civil servant Samuel Fennan has killed himself following a routine security check.

Because Fennan did not have a private office, Smiley had suggested the interview take place in an informal manner on a lunchtime walk through London.

He obtains information from telephone exchange staff that confirm it was Fennan who had requested the call the night before, furthering Smiley's suspicion around Elsa.

Pretending to be part of a laundrette delivery service, he avoids entering his house, and notes the number plates of the seven cars parked in the road.

Scarr, a semi-professional criminal, tells Mendel that he rents the car out on anonymous agreement to a stranger known as "Blondie", who matches the description of Smiley's intruder.

Smiley then realises that Elsa, not Samuel, is the East German spy, and that the accusation about Fennan had been self-composed in order to allow him to meet someone with whom he could discuss his concerns about his wife.

Back on bed rest in Mendel's house, Smiley turns down Maston's offer to reinstate him to the Circus with a promotion, and flies to Zürich in the hope that he can repair his relationship with Ann.

It was directed by Sidney Lumet from a script by Paul Dehn, and starred James Mason as Charles Dobbs, (not George Smiley, as le Carré had sold the rights to use the name "George Smiley" to The Spy Who Came in from the Cold), Harry Andrews as Mendel, Simone Signoret as Elsa Fennan and Maximilian Schell as Dieter Frey.

The major change in the script from the book is the addition of an affair between George's wife Ann and Dieter Frey, which presages the events of Tinker Tailor Soldier Spy.

Other characters and actors are as follows; Inspector Mendel—Kenneth Cranham, Elsa Fennan—Eleanor Bron, Ann Smiley—Anna Chancellor, Peter Guillam—Richard Dillane, Maston—James Laurenson, Dieter Frey—Henry Goodman, Adam Scarr/Mundt—Sam Dale, Ludo Oriel—Janice Acquah, Nursing Sister—Caroline Guthrie with Benjamin Askew and Jonathan Tafler.