When the Vatican observatory Priest sees a comet, the Church is sure that it confirms the eve of Armageddon. Meanwhile, the U.S. President's godson, Robert Thorn (Liev Schreiber), is informed in the maternity ward in Rome by Father Spiletto (Giovanni Lombardo Radice) that his wife Katherine (Julia Stiles) has just lost their baby and will not be able to get pregnant again. Spiletto suggests to Robert that another newborn child, whose mother has died, could be the substitute for his son, and Robert accepts the child and names him Damien. Robert is promoted to ambassador in London after a tragic accident. When Damien's nanny (Amy Huck) commits suicide during his birthday party, a substitute, Mrs. Baylock (Mia Farrow), comes to work and live with the family. Through the years, Katherine realizes that Damien is evil, while Robert is contacted by Father Brennan (Pete Postlethwaite), who tells him that Damien is the son of the devil. When the Priest dies in a bizarre accident, photographer Keith Jennings (David Thewlis) shows evidence to Robert that the boy is the Antichrist. They travel to the town of Megiddo to learn how the boy can be stopped.