In Rome, American diplomat Robert Thorn is in a hospital where his wife Katherine gives birth to a boy, who—he is told—dies. Moments after Robert is informed of a plan by the hospital chaplain, Father Spiletto, to secretly adopt an orphan whose mother died giving birth to him. Robert agrees, but does not reveal to his wife that the child is not theirs. They name the child Damien Thorn.
A week after the The Omen, archaeologist Carl Bugenhagen (Leo McKern) learns of the survival of their adopted son Damien Thorn. Confiding to his friend Michael Morgan (Ian Hendry) that Damien is the Antichrist, Bugenhagen attempts to convince him to give Damien's guardian a box containing the means to kill Damien. As Morgan is unconvinced, Bugenhagen takes him to some local ruins to see the mural of Yigael's Wall, which was said to have been drawn by a monk who saw the Devil and had visions of the Antichrist as he would appear from birth to death. Though Morgan believes him upon seeing an ancient depiction of the Antichrist with Damien's face, both he and Bugenhagen are buried alive as the tunnel collapses on them.