As the tension of the Cold War is peaking in 1973, George Smiley, former senior official in Britain's Secret Intelligence Service (known as "the Circus" because its London office is at Cambridge Circus, is living unhappily in forced retirement, following the failure of an operation codenamed Testify in Czechoslovakia, which ended in the capture and torture of agent Jim Prideaux. Control, chief of the Circus, had suspected that one of the five senior intelligence officers at the Circus was a Soviet mole, and had assigned them code names for Prideaux to relay back to the Circus, derived from the English children's rhyme "Tinker, Tailor".