What a mess! This serial has 3 major faults.

First, the premise is lame. A mad scientist (Stanley Price) known only as Phantom Ruler invents an incredibly bulky, and therefore difficult to transport, ray gun. This device will render an individual invisible when he or she is wearing clothes soaked in some sort of chemical solution. His plan is to steal $250,000, and use it to create a private army of invisible soldiers to overthrow the government of the US. Even in 1950 bucks, 250k was not enough to fund a coup de tat. The ray guns are so difficult to move about that they would be useless on the battlefield.

Second, Price (in the role of the leading villain) does not project anything resembling menace or authority. George Meeker, who plays one of Price's henchmen) had a long career in films. He often played smooth talking hoodlums. Meeker, I believe, probably was a better choice to play Phantom Rule.

Third. The photography is crisp and clear but does nothing to help create an aura of danger, intrigue, mystery etc.

This serial was made after Republic Studios adopted a policy of limiting all serial episodes to a running time in the 13 minute range. This keeps the action moving at a brisk pace and is a welcome innovation. This is the serial's one true strength and the only reason I awarded four stars (instead of three) to this film.

It shouldn't take long to find a better serial than Invisible Monster next time you are in the mood to watch a chapter play. I heartily recommend that you do so.