Fester's working on a new experiment when something goes wrong. An organ grinder's chimp wanders into the house when Fester's experiment blows up. Pugsley was watching, and was knocked through a wall. When the smoke clears, Fester sees the chimp and thinks he's transformed Pugsley into the chimp. Morticia thinks the chimp is nice, but wants her son back. Fester tries contacting the spirit world for advice. Pugsley and tries to explain to Fester that he's behind a secret door. He's eventually freed and the chimp returned to his owner. Wednesday turns up with a new boyfriend - the invisible man's invisible son.