Tinker Tailor Soldier Spy by John le Carre
A mole, implanted by Moscow Centre, has infiltrated the highest ranks of the British Intelligence Service, almost destroying it in the process. And so former spymaster George Smiley has been brought out of retirement in order to hunt down the traitor at the very heart of the Circus - even though it may be one of those closest to him. The first part of le Carre's acclaimed Karla Trilogy, Tinker Tailor Soldier Spy sees the beginning of the stealthy Cold War cat-and-mouse game between the taciturn, dogged Smiley and his wily Soviet counterpart.