在这部伦敦间谍战惊悚/剧情片中,英国外交部高官费农被匿名信告密是间谍，调查员查尔斯奉命对他约谈，不料费农即自杀死亡。查尔斯从种种迹象发现费农并非自杀，于是他展开个人调查。在一名精明的老刑警协助下，引诱出费农夫人的真面目，并惊异地发现幕后还有一双黑手在操纵她丈夫经手的国家机密。
After Charles Dobbs, a security officer, has a friendly chat with Samuel Fennan from the Foreign Office, the man commits suicide. An anonymous typed letter had been received accusing Fennan of being a Communist during his days at Oxford and their chat while walking in the park was quite amiable. Senior officials want the whole thing swept under the rug and are pleased to leave it as a suicide. Dobbs isn't at all sure as there are a number of anomalies that simply can't be explained away. Dobbs is also having trouble at home with his errant wife, whom he very much loves, having frequent affairs. He's also pleased to see an old friend, Dieter Frey, who he recruited after the war. With the assistance of a colleague and a retired policeman, Dobbs tries to piece together just who is the spy and who in fact assassinated Fennan.
