Dr. Lamarck Mondrick, a famous anthropologist, has just returned to the United States from the Gobi Desert with a mysterious box, the contents of which purportedly hold the key to humankind’s struggle between good and evil. Among journalists covering the anthropologist’s return is the protagonist, Will Barbee, who is both a close personal friend and a former member of Mondrick’s research team. Mondrick dies mysteriously while attempting to deliver a warning of a menace to the human race.
As the story progresses, researchers Nick Spivak and Sam Quain employ increasingly tight security measures to protect themselves and the mysterious box they guard, but to no avail. Spivak and Quain know that Barbee is, at the very least, genetically predisposed to be a werewolf. Rowena Mondrick, the anthropologist’s widow, knows for certain that Barbee is a deadly threat to her and the other two. She nevertheless has a true affection toward him. In the last chapter of the novel, author Jack Williamson reveals that she is Barbee’s mother.
By day, Barbee tries to find out who is doing the killing and why. By night, he is a werewolf who participates in the killing. The daytime Barbee is aware only on the subconscious level of the activities of the nighttime Barbee. During the day, he falls in love with a beautiful, young, redheaded journalist, April Bell, who also is assigned to the Mondrick case. At night, she becomes a werewolf who has little difficulty getting Barbee to do most of the killing for her.
The second, dominant, aspect of the plot is purely psychological. The human (good) side of Barbee battles the werewolf (evil) side for the ultimate possession of his soul. One side is destined to prevail. As events unfold, Barbee is shown to be literally the messiah the werewolves of the world have been hoping for, the one they have named in advance “The Child of Darkness.” Barbee does not know this and does not even fully comprehend that he is, in fact, a werewolf. His gradual self-realization is the main focus of the book. At the conclusion, having (sometimes reluctantly) participated in the killing of all the members of Mondrick’s research team and his own mother, Barbee fully accepts himself as a werewolf and thus as evil.