When he is summoned by the Cabinet watchdog for Intelligence Affairs, George Smiley agrees to return from retirement to head the hunt for a Secret Service mole.

Smiley is forced to go back over some very old ground when he is told a story about spies by old friend Ricki Tarr.

In his search for the mole sitting at the heart of the Circus, George Smiley sets out for Oxford to visit an old and invaluable friend.

Smiley recalls the past and his involvement with Tinker, Tailor, Soldier and Poorman; he also remembers Karla, the legendary head of Moscow Circus.

Smiley thinks that the time has come to call on Jim Prideaux, whose assignment to Czechoslovakia went disastrously wrong, with the mole at the heart of the Circus to blame.

Smiley's investigation to snare the traitor at the heart of the Circus leads him to Jerry Westerby, a Fleet Street journalist.