During the Cold War, the world's two major spy organizations, the Russian "Center" and the British "Circle", fought openly and secretly. The agent was killed, and the top leaders were furious and ordered the "Circle" to dig out the "rat". There were five suspects, namely the potter, tailor, soldier, poor man, and beggar named by the previous "boss" of the Circus. Among them, George Smiley (Gary Oldman), a "beggar" who had retired from the underworld, was originally a major suspect. One day, Peter Guillam (Benedict Cumberbatch), the leader of the action group-scalping group, and Lacon, the intelligence director of the British Cabinet Office, ruled out Smiley's suspicion and ordered him to come out again to dig out the "rat". So, Smiley began to visit old friends one by one, investigating the boss of the "Circus", Alleline, the tailor - Bill Haydon (Colin Firth), the soldier - the senior spy in charge of Eastern European affairs Roy Brand, the poor - the leader of the street lamp team in the logistics department Toby Esterhase. For a time, the Circus was full of doubts, and everyone was in danger. Who is the "mole"... This film is adapted from the novel of the same name by John le Carré. The title comes from the British folk "Mother Goose Nursery Rhymes".