Plot
George Smiley, deputy to the head of 'the Circus', has been forced into retirement in the wake of Operation Testify, a failed spy mission in Czechoslovakia. The Chief of the Circus, known only as Control, had sent veteran agent Jim Prideaux to meet a Czechoslovak general who supposedly had information identifying a deep-cover Soviet spy planted in the highest echelons of the British Secret Intelligence Service—known as the Circus, because of its headquarters at Cambridge Circus in London.
The mission proved to be a trap, and Prideaux was shot in the back, captured and tortured by the Soviets. Control was disgraced by Testify and replaced by his rival Percy Alleline. Control's obsession with the possibility of a Soviet mole at the Circus was not shared by others in the organisation, who insist that any leaks and failures at the Circus were due to Control's incompetence. On the contrary, Alleline and the rest of the new leadership team at the Circus believe that they have a mole, code-named Merlin, working for them in Moscow Centre, the KGB headquarters, passing them secrets in an operation code-named Witchcraft. Others in the British and American intelligence communities have been impressed with the information produced by Witchcraft, and Alleline and his team are regarded as a refreshing change from Control.
More than a year after Testify and the shake-up at the Circus, Ricki Tarr, a British agent gone missing in Lisbon, turns up in England with new evidence backing up Control's theory of a mole at the Circus. While on a routine mission Tarr had been approached by Irina, a low-level Soviet agent who claimed to know the identity of the mole and wanted to trade it for permission to defect. As soon as Tarr informed the Circus of Irina's offer, she was abducted by the KGB and spirited back to Russia. Tarr, convinced he had been betrayed by the mole Irina was going to identify, believed that he would also be targeted and murdered. Returning to London secretly, Tarr contacts Oliver Lacon, a senior civil servant who is the liaison between the Circus and the British Cabinet.
Before his ousting, Control had narrowed his list of suspects to five men – Roy Bland, Toby Esterhase, Bill Haydon, Percy Alleline and Smiley – all of whom occupied high positions in the Circus. Knowing the Soviet spy is highly placed in the Circus, Lacon cannot trust the Circus to uncover the mole or even allow its personnel to know of the investigation. Smiley, who had been fired along with Control while Control's other four suspects were promoted, is recalled by Lacon and given instructions to expose the mole. With the help of his protégé, Peter Guillam, who is still in the Circus, Smiley begins a secret investigation into the events surrounding Operation Testify, believing it will lead him to the identity of the mole, whom Moscow Centre has given the cover name Gerald.
Smiley learns that Operation Witchcraft uses a safehouse to meet with Aleksey Aleksandrovich Polyakov, a Soviet agent. Polyakov appears to hand over valuable intelligence material but this is actually "chickenfeed", and the operation is a cover by which Gerald passes valuable material to Polyakov. Smiley forces Toby Esterhase to reveal the location of the safe house. Tarr is sent to Paris, where he sends a coded message to Alleline about "information crucial to the wellbeing of the Service". This triggers an emergency meeting between Gerald and Polyakov at the safehouse, where Smiley and Guillam lie in wait.
The mole is revealed to be Bill Haydon. Haydon is debriefed by Smiley, but is killed by Jim Prideaux before he can be exchanged with the Soviets.
