The Mad Botanist is a genius with varying genera of deadly plants. He uses an African Tentacle Vine to strangle Mr. Allen, to death while Captain Flag valiantly works to save the inventor’s life. He then sets his sights on Allen’s inventor partner, Mr. McCoy. FBI agent Veronica Darnell is ordered by her superior to protect McCoy. She first takes a detour to assist Captain Flag to escape from jail, where he has been placed on suspicion of Allen’s murder.
Veronica then goes with McCoy to a premiere with tickets that the Diabolical Botanist sent him.
Outside the event, the Botanist, disguised as Rose, the Broadway Flower Peddler, approaches Darnell and McCoy. The botanist offers a corsage to McCoy, which the inventor allows to be pinned to his coat. Veronica skips McCoy’s offer of a corsage for her.
The flower is actually a Mediterranean Poison Cornflower. McCoy soon becomes ill from the toxic plant. Captain Flag arrives. Seeing what is going on, he instructs Veronica to call an ambulance while he pursues the botanist. Flag confronts the Mad Botanist in the villain’s greenhouse. In the scuffle, the Mad Botanist falls into a Man-Eating Clam Plant, which gruesomely consumes him.