London, 1956. A generation of British spies are haunted by the ghosts of friends turned traitors. Henry Bone, a Mandarin spymaster, is convinced that a man code-named 'Butterfly' is the Holy Grail of Cold War Intelligence. In reality, however, Butterfly is an aristocratic pervert whose political tastes are as ugly as his sexual preferences. Worst of all, Butterfly has the ability to identify each traitor—and every serving British spy who helped them.