Simon Cordier (Vincent Price) is a well-respected magistrate, who chooses to visit a condemned prisoner, Louis Girot, on the eve of his execution.
Girot frenziedly pleads his innocence, vowing that a spirit named Horla, who took over his body and forced his hand, is truly responsible for the crimes he has committed. When Cordier shows no mercy and refuses to believe him, the man astoundingly perishes before his eyes! Over the following days, the magistrate bears witness to a number of peculiar happenings in his own home. At first, he believes he may be sleepwalking, but soon he starts to hear voices and fears for his sanity.
After taking up sculpting to soothe his anxieties, Cordier embarks on an affair with Odette (Nancy Kovack), a gold digger married to a struggling artist.
Will the couple find happiness, or will the wrath of the Horla strike again..?