After Kathy Thorn gives birth to a baby who doesn't survive, her husband Robert decides to protect her from this devastating truth. So, she replaces her child with an orphan, unaware of the child's satanic origins. The horror begins on Damien's fifth birthday when his nanny commits a dramatic suicide. Soon after, a priest who was trying to warn Damien's father is killed in a strange accident. As the death toll mounts, Robert realizes his son is the Antichrist and decides he needs to kill the boy to stop the terrible prophecy from being fulfilled.