A Russian mole has infiltrated the British establishment - and the spymaster Smiley must dig them out...

George Smiley, formerly of the Secret Intelligence Service, is contemplating his new life in retirement when he is called back on an unexpected mission. His task is to hunt down an agent implanted by Moscow Central at the very heart of the Circus - one who has been buried deep there for years. The dogged, troubled Smiley can discount nobody from being the traitor, even if it is one of those closest to him.