Maya Larkin (WINONA RYDER) is a young, devout woman who works with the Catholic Church in assisting Father Lareaux (JOHN HURT) and deacon John Townsend (ELIAS KOTEAS) in performing exorcisms of those who are possessed by demonic spirits. A former victim herself, Maya and her team arrive at a psychiatric hospital to perform such a ritual on Henry Birdson (JOHN DIEHL), a convicted mass murderer.
The results leave Lareaux incapacitated and Maya attempting to decipher a numerical code that Birdson had been compulsively penning. When she finally does so, the code reveals that the next victim of possession will be Peter Kelson (BEN CHAPLIN), an author and self-proclaimed cynic of evil with a capital E, who writes about mass murderers such as his latest subject, George Viznik (BRAD GREENQUIST).
Peter, who was raised along with his brother, William (W. EARL BROWN), after their parents' deaths, by their uncle, Father James (PHILIP BAKER HALL), doesn't believe in any of what he thinks his pure nonsense. Nonetheless, he doesn't tell his girlfriend, Claire Van Owen (SARAH WYNTER), although she gets the hint when someone tries to kill him one evening, proclaiming that the time of transformation has come.
With friend and local detective Mike Smythe (JOHN BEASLEY) investigating that incident as well as Maya's background, Peter tries to get on with his life. Yet, as strange events begin occurring all around him, it appears that perhaps he is earmarked to become the Antichrist. As such, he and Maya then race against time in an effort to make sure that doesn't happen.