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Tear Jerker: Tinker, Tailor, Soldier, Spy
Smiley's promise to Ricky Tarr that he will do his best to get her back, when the viewer knows this is hopeless, and Smiley strongly suspects as well.
Jim Prideaux's story arc. Shot down in Hungary, brutally tortured in Russia, then sent to work as a schoolmaster in England, where he meets a nice Morality Pet student, only to push him away. Finally he learns for certain that his best friend/maybe lover Bill Haydon is the mole, and kills him.
In the mini-series, Smiley's interview with Connie Sachs.
"Poor loves. Trained to Empire, trained to rule the waves. Englishmen could be proud then. They could, George. All gone, taken away. Bye-bye world. If it's bad, George, don't come back. Promise? I want to remember you, just as you were. My lovely, lovely boys..."