President's godson Robert Thorn is informed in the maternity in Rome by Father Spiletto that his wife Katherine has just lost her baby and she had troubles with her uterus and would not have another pregnancy. Spiletto suggests Robert that another just born child that lost his mother could be the substituted for his son, and Robert accepts the child and gives the name of Damien. Robert is promoted to ambassador in London after a tragic accident. When Damien's nanny commits suicide in his birthday party, a substitute, Mrs. Baylock, comes to work and live with the family. Along the years, Katherine realizes that Damien is evil, while Robert is contacted by Father Brennan, who tells him that Damien is the son of devil. When the priest dies in a bizarre accident, the photographer Keith Jennings shows evidences to Robert that the boy is the Antichrist. They travel to the town of Megiddo to learn how the boy can be stopped.

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