 The castaway William Fitzgerald (Richard Derr) is rescued in an island by Dr. Charles Girard (Francis Lederer), his lonely wife Frances Girard (Greta Thyssen) and his assistant Walter Perrera (Oscar Keesee Jr.). A couple of days later, Fitzgerald has an affair with Frances and realizes that the unethical and insane Dr. Girard is developing sick experiments and transforming a panther into a man-like creature. Meanwhile, the monster escapes from the laboratory, killing Walter and the servant Celina and seizing and capturing Frances with him. Fitzgerald and Dr. Girard chase the being along the night.