George Smiley, the aging master spy of the Cold War and once heir apparent to Control, is brought back out of retirement to flush out a top level mole within the Circus. Smiley must travel back through his life and murky workings of the Circus to unravel the net spun by his nemesis Karla 'The Sandman' of the KGB and reveal the identity of the mole before he disappears.

Called out of retirement to settle the affairs of a friend, Smiley finds his old organization, the Circus, so overwhelmed by political considerations that it doesn't want to know what happened. He begins to follow up the clues of his friends past days, discovering that the clues lead to a high person in the Russian Secret service, and a secret important enough to kill for.