With the Cold War at it's height, the head of the British counter-espionage agency - "Control" (Alexander Knox) is giving a clear impression that he is losing the plot. He is visibly ailing so his subordinates gather like vultures waiting to take his place. His preferred candidate is the redoubtable, semi-retired, "Smiley" (Sir Alec Guinness) and pretty swiftly we discover that is because the old man is not so doting after all, and is suspicious that there is a spy in his midst. Who can he trust to investigate the matter? There were seven parts to this BBC drama and each episode delivers some ...