Mad Scientist Anton Arcane sends his henchmen to capture Swamp Thing, who he thinks he can use to discover the secret of eternal life. They fail miserably so Arcane subjects them to his Transducer machine, which turns them into monstrous Un-Men.
Meanwhile, J.T. and Delbert are in the swamp trying to catch frogs to sell them. They're attacked by the Un-Men, who Swamp Thing shows up and battles. Swamp Thing manages to defeat Skin Man, but the boys think he's just another monster who wants to eat them and run away. They're captured by Dr. Deemo and taken back to Arcane's plantation. There they meet Abigail Arcane, a friend of Swamp Thing's, who tells them his story. He was once Alec Holland, a scientist. Arcane tried to force him to help find the secret of immortality, but Holland refused. Arcane destroyed his laboratory, and covered in chemical Holland dove into the swamp and became a hybrid of man and plant.
Arcane threatens to do horrible things to the boys unless Swamp Thing surrenders himself for experimentation, and Swamp Thing does so. Arcane sucks out his vital fluids, turning Swamp Thing brown and weak. His allies Tomahawk and Bayou Jack storm the Arcane plantation and save him, and in the process of their escape the serum Arcane was draining is destroyed and Arcane himself is splattered with chemicals, turning him into a mutated freak. Arcane tries to shoot the fleeing heroes with a mutation spray, but Swamp Thing grows a protective layer of leaves and absorbs the mutagen, allowing them to escape.
- This episode had a few differences to later ones, such as Weedkiller being able to stick walls, and Dr. Deemo only speaking in rhymes a few times while usually speaking normally.