Inspector Clouseau and his sidekick, Sergeant Deux-Deux, investigate an old house in the Rue Morgue section of Paris after having arrested its tenant, a mad scientist, for causing interference on neighbors’ TV sets. Clouseau is convinced there is a monster loose on the premises, especially after Deux-Deux, when Clouseau wasn’t looking, drank a bubbly potion from a beaker and turned into a horrible creature. Deux-Deux keeps changing back and forth, burping before each transformation, and not remembering anything he did in the interim. Finally, Clouseau realizes that Deux-Deux is the creature and flees the house, with Deux-Deux chasing after him, changing into the monster at second intervals.