故事发生在1966年6月6日的上午6时,在这样一个不吉利的时刻,美国大使罗伯特(格利高里·派克 Gregory Peck 饰)领养了一个男孩并取名戴米(哈维·史蒂芬斯 Harvey Stephens 饰)。随着时间的推移,戴米渐渐长大,一些奇怪事件的接连发生预示着厄运敲响了罗伯特的家门。 戴米的保姆莫名自杀后,一个神秘的女人贝洛克(比莉·怀特劳 Billie Whitelaw 饰)毛遂自荐留在了戴米的身边。之后,神父博南(帕特里克·斯偌顿 Patrick Troughton 饰)找到了罗伯特,他告诉罗伯特,戴米是撒旦的孩子,戴米会不择手段完成统治世界的野心。对于神父的话,罗伯特半信半疑,直到博南神父的死讯传来,罗伯特才意识到,事态的发展是多么的糟糕。Robert and Katherine Thorn seem to have it all. They are happily married and he is the US Ambassador to Great Britain, but they want nothing more than to have children. When Katharine has a stillborn child, Robert is approached by a priest at the hospital who suggests that they take a healthy newborn whose mother has just died in childbirth. Without telling his wife he agrees. After relocating to London, strange events - and the ominous warnings of a priest - lead him to believe that the child he took from that Italian hospital is evil incarnate.