He has to spy on the spies. And to expose the mole so that he doesn't expose himself.
The fiasco of Operation Testimony on the territory of normalised Czechoslovakia tells the top brass of London's MI6 that something is wrong inside. In the early 1970s, a double agent or "mole" controlled by Moscow was running amok at the headquarters of their intelligence service. The new collective leadership of the institution will therefore call in a person who was until recently unwanted: the prematurely retired, wife-betrayed but seasoned Cossack George Smiley.
It is up to him to investigate with ant-like diligence and bulldog-like vigour to whom the threads of betrayal lead. An espionage fresco from the era of classic telephones, microfilm and dead boxes, in which ordinary agents earn a much more prosaic living than the supermen in Bond films, it exposes the gears of the intelligence headquarters known as the Circus. Smiley and his men have no choice but to unleash a series of subterfuge, as all indications are that the strings of the conspiracy lead to one of their superiors...
The genre's most famous classic novel was made into a film for the second time in 2011, starring Gary Oldman, Toby Jones, Colin Firth, Benedict Cumberbatch and Tom Hardy. However, unlike its subject, Swedish director Tomas Alfredson's film, with its impressive Nordic-style production design, begins with a fiasco in Hungary.