In New England Cap and Bucky discover a Nazi plot to obtain Zorite, a new metal that makes plane and tanks more fuel efficient. When two state dept. geologists are found dead, a "shadow monster" is blamed for the killings. The Nazis have found out about a local painter who is painting shadows in the act of committing murder and are setting him up to be the fall guy so that no one will realize the Nazis have discovered and are mining the Zorite vein. Cap chases the truck leaving the quarry with the metal and pounds the driver in the face. Rather than be sent to death as a spy, the driver heads off the cliff attempting to kill both Cap and himself, but Cap leaps free of the truck.