King Julien is taken to the hospital after showing strange behavior, so Maurice is left in charge. But Maurice soon develops the same behavior, and begins to rule the zoo with an iron fist. It's up to the penguins and King Julien to stop Maurice before he takes over the zoo then New York.
As the penguins play a game of "Stomp the Wombat", they suddenly hear a hysterical laughing noise coming from outside. Private initially assumes it was a hyena, but, remembering that they don't have a hyena exhibit at the zoo, the penguins investigate and find that the laugh is coming from King Julien. He has gone crazy and has red eyes. He is taken to the zoo doctor and Maurice is put in charge per Skipper's request. Maurice eventually eats Julien's red Lychee nuts and becomes power crazy himself. A red-eyed Maurice becomes a tyrant and demands that all the animals swear their eternal loyalty to him.
Maurice cuts off the power for all of the other habitats when his demands are not met by the penguins, as Skipper assumes he was joking. At this point, the penguins break into the control room with the intent of restoring power only to be caught in traps. Maurice has his new gorilla bodyguards, Bada and Bing, hang the penguins up in front of his throne, but Skipper cuts himself and the others loose with a playing card.
The penguins go to the animal care building and find King Julien doing well. As Kowalski examines the Lychee nuts, he discovers them to be the cause of Maurice's recent behaviour. He reveals that when they go bad, they release an enzyme that amplifies aggression in the brain. He also finds that guava-berry juice counteracts the Lychee nuts enzymes which intensify aggression. Kowalski stores some of the juice in aerosol form and they head back to cure Maurice.
When the penguins arrive they announce their intentions to Maurice and as a result are sent flying into a wall when they unsuccessfully attempt to spray Maurice. Mort gets the can and cures Maurice and all is well.
Mort is seen eating the remaining three nuts at the end, his eyes glowing red.