Long-suffering spy Bernard Samson has, against all the odds, enticed a Soviet agent to defect to London - but this proves to be the start of something even bigger. For he learns that there is treachery within his own Service, and no one is free from suspicion. To discover who really controls the game of spies, he must attempt a desperate gamble. As the Game, Set and Match trilogy reaches its shattering finale, who will make the winning move?