二战后,美国作家马丁(约瑟夫•科顿 Joseph Cotten 饰)应好友哈里(奥逊•威尔斯 Orson Welles 饰)邀请到维也纳工作,岂料刚到达目的地就传来了哈里车祸身亡的消息。哈里葬礼上,马丁遇到了当地军官卡洛维,卡洛维很不客气的请他马上离开维也纳。马丁没有理会,决心留下调查出好友死亡的真相。 马丁找到哈里的女友斯科姆特小姐(阿莉达•瓦莉 Alida Valli 饰)一起调查事件的真相。随着调查的深入,他们发现内幕越加扑朔迷离,首先是他们的房东遇害,接着马丁自己发现被人跟踪,而且他查出哈里死的时候还有个第三人在场。于是,一切关键就在于找出这个神秘的第三人。An out of work pulp fiction novelist, Holly Martins, arrives in a post war Vienna divided into sectors by the victorious allies, and where a shortage of supplies has lead to a flourishing black market. He arrives at the invitation of an ex-school friend, Harry Lime, who has offered him a job, only to discover that Lime has recently died in a peculiar traffic accident. From talking to Lime's friends and associates Martins soon notices that some of the stories are inconsistent, and determines to discover what really happened to Harry Lime.