George Smiley's quiet retirement is interrupted when messengers arrive from London Station and call upon George Smiley to come back into the game. Smiley is brought to Sir Oliver and is revealed that a highly influential mole has been operating out of the Circus for quite some time.

Ricki Tarr, an active agent, recounts a tale to the spy masters that sways Smiley in favour of returning to the Circus to secretly ferret out the mole. Tarr's tale is of The Sandmann, the KGB counterpart and nemesis of Smiley, and of his network in the Circus.

Now that Smiley has rejoined the game he must secretly procure the information and files needed to conduct his investigation. While Peter breaks into the Circus' archives and finds files that bring a whole new perspective to consider, Smiley goes to interview an old friend.

Ricki Tarr becomes unstable and George Smiley must examine his past to find answers. He must examine his personal life as well as his past with the Circus, especially in regard to Control. He also reflects on his meeting with Karla, 'The Sandman'.

Smiley, now fortified with new information, goes to confront Jim Prideaux, an old spy who long since came in from the cold and is now a school teacher. Control, in his last days, seemed to have confided in him and sent him on a mission behind the Iron Curtain to find out who exactly the mole in the Circus was, Tinker, Tailor, Soldier, Rich man, or Poor man.

Smiley now has the information he needs and starts to stir things up with the men of which Control suspected one to be the mole. He is able to eliminate two, himself and one other. The waiting begins, when suddenly the message arrives that Prideaux has disappeared.

The waiting has paid off and the traps closes on Karla's mole. It is agreed to trade him against several English spies who were captured by the KGB, but Prideaux is still not found and he has an open account to settle with the mole. With the command structure of the Circus hollowed out and containment in progress, Smiley cannot come in from the cold but remains to pick up the pieces.

In his first television interview for 15 years, Mr Le Carre admits he started working for the secret service when he was 16 and went on to become a senior undercover operative in West Germany at the height of the Cold War. It is the first time the author, whose books include Tinker, Tailor, Soldier, Spy, has explicitly confessed to having been a spy. The interview features in John Le Carre: The Secret Centre, a documentary about the author's life to be broadcast on Boxing Day 2000 on BBC2. In the programme Le Carre describes how he first became involved with foreign intelligence after running away to Switzerland to escape the influence of his father, a confidence trickster. While living in Berne he met an MI6 official from the British consul and began running errands for him. Le Carre, whose real name is David Cornwell, returned to England after a year but maintained contact with the secret services while studying at Oxford University and later, as a teacher at Eton, before joining MI5 full-time. He was transferred to MI6 and dispatched to West Germany, where, according to his first wife, Anne Martin, he spent several years "deep undercover". Le Carre says his career in espionage came to an abrupt end in 1963 following the publication of his first spy novel, The Spy Who Came in from the Cold. Le Carre has always been guarded about his spying career, although it was understood to have informed much of his writing. Nigel Williams, the documentary's maker, said he thought Le Carre had decided it was time to come clean about his past: "He is a highly patriotic Englishman and he hadn't talked about it before because he thought it wasn't right to do so. But he is almost 70 now and I think he felt he should set the record straight."