A small group of Catholics led by an ailing priest believe that Satan intends to become man, just as God did in the person of Jesus. The writings of a possessed mental patient lead them to Peter Kelson, a writer who studies serial killers. They think it's his body Satan will occupy. The youngest in the group, a teacher named Maya Larkin, goes to Peter to investigate further and to convince him to believe in the possibility of Evil incarnate. Other signs come to him as he and Maya them take a journey full of strange occurrences, self-discovery, and an ultimate showdown.