After a routine security check by George Smiley, civil servant Samuel Fennan apparently kills himself. When Smiley finds Circus head Maston is trying to blame him for the death, he begins his own investigation, meeting Fennan's widow to find out what led him to such desperation. On the very day Smiley is ordered off the enquiry he receives an urgent letter from the dead man. Do the East Germans - and their agents - know more about this man's death than the Circus previously imagined?