A wealthy American diplomat agrees to adopt an orphaned child when his own son is delivered stillborn in a Rome hospital. Five years later, his idyllic life as US Ambassador in London is shattered when a series of sinister deaths persuades him that his child is not what he seems.
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.