The arrival in a small mountain town of a dissheveled stranger launches a series of murders committed by some sort of animal. As the town doctor and his daughter attempt to help the stranger, the sheriff investigates the murders; and they uncover a sinister experiment involving two rogue scientists, a car accident victim, his wife and children, and a serum that causes a man to turn into a ravaging werewolf.

Wanted outlaws have mysteriously disappeared. Ranger Captain Henley and Steve have a plan to find them. Steve becomes a wanted man by faking the killing of Henley. Not only is he now in trouble as both the Rangers and the Mexican Rurales are after him, but Smiley knows him and may expose his masquerade to the bad guys.

Rival reporters (George Brent, Joan Blondell) investigate a Hollywood star (Adele Jergens) and the box she receives with a dead man inside.