Tinker Tailor Soldier Spy

Many employees of the British investigation guessed that the "mole" working for Russia sat down at its management long ago. But those who ventured to declare it openly, for some reason appeared in resignation. The others preferred to keep mum. But confirmation of existence of the Russian agent came from absolutely unexpected side. The secret investigation headed by George Smiley who is in resignation begins. And anybody, including the top management of investigation, shouldn't guess that on a mole hunting is again declared.
In the bleak days of the Cold War, espionage veteran George Smiley is forced from semi-retirement to uncover a Soviet mole within his former colleagues at the heart of MI6.