The Invisible Monster

In this 1950 Republic film serial, a man-woman team of investigators must stop a gang led by a mad scientist known only as The Phantom Ruler, who has developed an invisibility chemical that could be used to build a mercenary army of invisible men. With the help of an investigator from a bank's insurer and a woman police detective, they track down clues and thwart the villain's attempts to rob banks while invisible. In the end, the heroes expose The Phantom Ruler's plan and bring him to justice in a thrilling finale that involves some high-voltage danger.