医生米尔斯·本耐尔(Kevin McCarthy 饰)正出差参加一个医学会议,期间他接到护士(Jean Willes 饰)的电话,称其所在的小镇病患激增,本耐尔医生只得匆匆赶回。但是小镇的情况却让他心生疑虑,当本耐尔回来时发现,大多数的门诊预约已经取消,而前来看病的患者则令其备感陌生。虽然病人们能一一说出小镇上的生活细节,然本耐尔却总认为他们并非原来的居民。 不久本耐尔的朋友杰克(King Donovan 饰)和泰迪(Carolyn Jones 饰)组织了一个派对,聚会上,本耐尔终于发现了他百思不得其解的事实真相……Dr. Miles Bennell returns to his small town practice to find several of his patients suffering the paranoid delusion that their friends or relatives are impostors. He is initially skeptical, especially when the alleged dopplegängers are able to answer detailed questions about their victim's lives, but he is eventually persuaded that something odd has happened and determines to find out what is causing this phenomenon. This film can be seen as a paranoid 1950s warning against those Damn Commies or, conversely, as a metaphor for the tyranny of McCarthyism (or the totalitarian system of Your Choice) and has a pro- and epilogue that was forced upon Siegel by the studio to lighten the tone.