Dr. Carl Stoner, a
herpetologist, sells a mysterious creature in a crate to a carnival owner. He hires college student David Blake as an assistant, claiming that his previous assistant had left town to attend to a sick relative. Unbeknownst to David or anyone else, Stoner is a delusional man. Stoner begins David on a course of injections, purportedly as a safeguard against being bitten by a snake in his lab. David's skin slowly starts to change and even peel like a snakeskin. He begins to have strange nightmares and goes into a
coma when having dinner with Stoner, not waking up until a few days later. He also begins to lose weight, but Stoner tells him those are side effects from the venom. David begins a romance with Stoner's daughter Kristina. Her father objects and insists that she not have any sexual relations with him, not knowing that she already has. When David wakes up the next morning, he has become green and covered with scales. Stoner takes him to the lab and gives him another injection. Stoner's colleague, Dr. Daniels, arrives to inform him that he has been denied an extension of his research grant. Stoner reacts to the news with indifference. Made suspicious by this, Daniels inspects the property. Stoner hides David in a corner, but David gets enough strength to walk to a window, allowing Daniels to see him. Stoner knocks Daniels out and feeds him to a
python, and David collapses. Kristina visits a carnival
freak show and sees a limbless "snake-man", whom she recognizes as Stoner's previous assistant. Horrified, she races back home to save David, who mutates into a
king cobra, brought about by Stoner's injections. Deeming his work a success, Stoner provokes a king cobra from his lab into biting him and dies. Kristina arrives home and finds her father's body with the cobra next to him. Growing suspicious, the police arrive and shoot the cobra before heading to the lab where a
mongoose is biting David's neck, attempting to kill him. As Kristina screams David's name, the movie ends, leaving their fates uncertain. ==Cast==