In attempting to develop a chemical which would make a person super-intelligent, Dr. Montrose fails and the subjects of his experiments metamorphose into hideous monsters who band together and prey on humans. With the police stymied, a young detective attempts to track down the leader of the group of killers, known only to have a small crimson stain in one eye.

Helen Merrill sings and dances in the rough Western mining town of Nugget City, where she befriends Myrtle Cadby, whose husband Jake cruelly abuses her. After a particularly vicious beating, Myrtle, seriously injured, shoots Jake. As she lies dying, she gives Helen a letter of introduction to a man she was to have married in the East, urging her to leave Nugget City. Before she leaves, Helen overhears Bill Sheridan and "Snipe" Roach scheming to sell Charles Taylor, a wealthy New Yorker, a salted mine, with the assistance of George Reed, Taylor's mining agent. Helen goes East and learns that Taylor is the man whom Myrtle was to have married, but because she immediately falls in love with him, she conceals her own identity and masquerades as Myrtle.