When Skipper is de-aged by one of the Kowalski's inventions, the other penguins must find a way to reverse its effects.
When Kowalski's ray designed to freshen spoiled food accidentally hits Skipper before falling down a storm drain, the leader is turned into a chick. He now possesses the strength, stamina, and needs of a chick, while retaining much of adult Skipper's personality, and is annoyed by the other penguins insisting how cute he is.
While the other penguins attempt to retrieve the ray, the down-feathered Skipper is baby-sat by Julien, under the story that he is "Petey," the penguins' little cousin, much to Skipper's displeasure.
After the other penguins find that the ray is in the possession of the sewer rats, they are captured by them. Sensing his team is in danger, baby Skipper slips past a sleeping Julien and enters the sewers, ultimately defeating the Rat King through quick-thinking leadership – and a flatulent emission called the "Baby Boom". With the ray back in Kowalski's possession, he returns Skipper to his normal self at the HQ.
- Rock-A-Bye Peety—Julien