Hal Westerfield in the California foothils encounters an ancient oak that appears to offer a window back into a primeval world. There he is subjected to horrific scenes of violence and depravity committed by an ape-like figure of a man who seems able to retain an identical form that spans the centuries--all the way into present one. There he becomes a prey animal, stalking Westerfield and his family. The terrifying events that follow tax Westerfield's credulity, and finally. in order to save him and his family require that he abandon conventional thought and enter a world that has no discernible parameters.