The head of Britain’s MI6, “the Chief,” suspects that one of his closest assistant agents is a KGB operative, and sets up a complex multi-step operation to identify the “mole.” The operation ends in a major failure. The “Chief” and his deputy Smiley are sent into retirement. Soon afterward, the “KGB agent in MI6” rumor seeps into the government, and the deputy minister, Leakon, is forced to ask Smiley to identify the “mole” and prevent an international scandal.