Set during the Victorian era, the film stars Peter Cushing as a Holmeslike detective on the trail of a serial killer. The mystery angle is minimal, since we know virtually from the beginning that the killer is a gigantic....moth! It seems that Wanda Ventham, daughter of addled scientist Robert Flemyng, has spent too much time in her dad's lab, and can turn herself into a malevolent moth at will. Flemyng tries to mollify Ventham by creating a playmate for her-and the result is two murderous moths. was also released as .