For reasons I cannot begin to fathom, Dr. Lorenzo Cameron (George Zucco) begins injecting wolf's blood into his dim-witted handyman, Petro (Glenn Strange). The result  Petro is transformed into a hideous (as hideous as someone with a bad wig and pointy teeth can be) killer beast. Dr. Cameron uses Petro to get his revenge against those in the scientific community who scoffed at and ridiculed his ideas (and why wouldn't they, Dr. Cameron's nuttier than a fruitcake).<br /><br />Overall, The Mad Monster is one dull and poorly made Poverty Row thriller. There's really only one positive I can come up with to write about in The Mad Monster. George Zucco can be fun to watch as he plays the mad scientist about as well as anyone. His Dr. Cameron is a regular loony. He has no qualms about killing; he has entire conversations with people who aren't there; and, as with most mad scientists, he messes in "God's domain" (actually, I'm not sure anyone accuses him of this, but it fits). But beyond Zucco, there's nothing here to recommend. Everything else from the monster effects to the supporting cast to the music is plain old bad. There are far better examples of Poverty Row horror from the 1940s than The Mad Monster.