Tinker Tailor Soldier Spy is considered to be amongst the finest spy literature of our time and comes as close to a faithful rendering of the Intelligence profession as possible.
The chief protagonist is the unassuming but brilliant George Smiley - who is called upon by the higher powers in the British Government to investigate a possible infiltration of the intelligence agency by Soviet moles. The rest of the plot is about Smiley's efforts to smoke out the mole through elaborate fact finding missions and interviews with his current and former colleagues in the intelligence agency.
The novel - typical of Le Carre's writing can best be defined as slow burn but the last few pages do pick up the pace while never veering into unbelievable or forced action thriller territory. While very intelligently written and a thorough novel with no loose ends, it's definitely not the best introduction to Le Carre's works. However for fans of his work - this is a must read.