The Plantman goes to the arctic and discovers three giant plant monsters from long ago. He takes them to his lab where he brings them back to life. He uses his control ray and puts them under his control. He decides that before he can begin his conquest, he must rid himself of his enemies, Buzz Conroy and Frankenstein Jr.
Plantman instructs his plants to break into the Conroy lab and steal Frankenstein Jr. and dump him into a lake. They then capture Buzz, but Buzz is able to get away and holds onto a vent at the top of the lab. He then signals Frankie to come and help. frankie shows up in the nick of time and he quickly defeats the first plant monster. Then another plant starts breathing flames and Frankie counters with more flames and defeats that one as well. Then Plantman attempts to escape and uses the last monster to try and defeat our heroes. He fails and is captured. The day is saved once again by Buzz and Frankenstein Jr.