Tinker Tailor Soldier Spy (1974)

George Smiley is recalled to investigate a Soviet mole inside British intelligence. The work consists of revisiting conversations, weighing reports and understanding colleagues whose habits once seemed reassuring. Its density is purposeful: the reader is given a structure to reconstruct, with betrayal changing the meaning of earlier details. Start here for the Karla trilogy, which continues with The Honourable Schoolboy and Smiley's People.