Episode 1

The head of the British Secret Service, code name Control, makes elaborate and secret arrangements to meet Jim Prideaux, one of his most trusted agents. Control wants Prideaux to go to Czechoslovakia to debrief a Czech general by the name of Stevcek. The general has agreed to pass on the name of a KGB 'mole' working in the upper echelons of the British Secret Service. Control has narrowed it down to one of his five most senior men and gives the names to Prideaux with code names that only the two of them will know: Percy Alleline (Tinker), Bill Haydon (Tailor), Roy Bland (Soldier), Toby Esterhase (Poorman) and Control's faithful deputy, George Smiley (Beggarman). Control tells Prideaux that he cannot provide any help if things go wrong as the operation is unofficial, but that all he needs is the code name to find out the real identity of the mole, who the Russians call 'Gerald'. Prideaux goes to the rendezvous in Czechoslovakia but the military is waiting for him. Prideaux tries to escape but is shot in the back and arrested.

A year later, George Smiley sees Peter Guillam, an old friend, in the street and goes out of his way to avoid him. Later, Smiley is accosted by another old colleague, Roddy Martindale, who insists on taking him for supper at his club. Martindale brings Smiley up to speed on what has been happening in the Service since Smiley was forced to leave and Control died. Alleline has now taken Control's job, with Haydon and Bland working as his main deputies, while Esterhase is doing jobs for the two of them. Roddy is embittered, convinced that Alelline couldn't possibly be responsible for his own success and that someone like Smiley must be helping him from behind the scenes. Smiley leaves angrily and goes home. There he finds Guillam waiting for him. Smiley is needed again and Guillam is there to collect him.

Guillam drives Smiley to a safe house to see Oliver Lacon, a senior advisor to the Service from the Cabinet Office. He takes them to meet Ricky Tarr, an operative previously stationed in Portugal, but now listed as absent without leave and on the wanted list. Tarr tells them that he has information which, if true, could completely change the Service.