The Spy Who Came in from the Cold is a 1963 Cold War spy novel by the British author John le Carré. It depicts Alec Leamas, a British agent, being sent to East Germany as a faux defector to sow disinformation about a powerful East German intelligence officer. It serves as a sequel to le Carré's previous novels Call for the Dead and A Murder of Quality, which also featured the fictitious British intelligence organization, "The Circus", and its agents George Smiley and Peter Guillam.
https://en.wikipedia.org/wiki/The_Spy_Who_Came_in_from_the_Cold