The Spy Who Came in from the Cold by John le Carré

Alec Leamas is tired. It's the 1960s, he's been out in the cold for years, spying in the shadow of the Berlin Wall for his British masters. He has seen too many good agents murdered for their troubles. Now Control wants to bring him in at last - but only after one final assignment. He must travel deep into the heart of Communist Germany and betray his country, a job that he will do with his usual cynical professionalism. But when George Smiley tries to help a young woman Leamas has befriended, Leamas's mission may prove to be the worst thing he could ever have done. In le Carré's breakthrough work of 1963, the spy story is reborn as a gritty and terrible tale of men who are caught up in politics beyond their imagining.