Ameriški zastopnik veleposlanika v Italiji Robert Thorn in njegova žena Katherine doživita tragedijo, ko se jima rodi mrtev otrok. Duhovnik v bolnišnici Robertu ponudi rešitev. Ker se je istega dne rodil tudi zdrav deček, čigar mati je umrla pri porodu, lahko dečka zamenja s svojim mrtvim sinom, tako da Katherine nikoli ne bi izvedela resnice. Robert privoli in tako z ženo postaneta ponosna starša sina Damiena. Pet let kasneje Thornovi živijo v Londonu, vsi ljudje, ki pridejo v stik z dečkom, pa po takšnem ali drugačnem naključju umrejo. Katherine je prepričana, da je Damien obseden z zlom.
When the Vatican observatory priest sees the appearance of a comet, the Church is sure that it confirms the eve of the Armageddon. Meanwhile, the USA 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.