"Rat Fink" is the thirty-ninth episode of season 2 from The Penguins of Madagascar.
The penguins were monitoring their enemies in five stations, including Alice in Station Alpha and Officer X in Station Delta. Their surveillance equipment monitoring the rats in an extra station, Station Zeta, became disabled, by vague words from the Rat King. Now, they are looking to put an undercover agent within the rats' sewer hideout. As penguins, their sizes and avian traits were not perfect to hide among the crowds of rats so they found Mort to be useful. They shaved the tail and put a speakerphone on him, and made the small lemur into thinking he was a rat. He infiltrated the hideout, learning that the rats were simply choosing carpeting colours (the Rat Kings refuses to choose Midnight Escape) but due to his childish nature, his cover was blown. Skipper, who was aided by a cover-blowing Julien, failed to get past the guards and find Mort to be not captured and imprisoned but hailed as a king. The Rat King stated he left the throne since Mort has a red birthmark which indicates he is rightful to the throne. When Mort tells the rats about how wonderful the surface world was, the former king thought that Mort wanted to start an invasion of the surface.
Meanwhile, the others start planning on getting in to rescue Skipper, Julien and Mort when the rats start invading. This starts becoming a problem as Mort no longer likes Julien's feet! Later it turns out the red mark on Mort's tail was actually strawberry jam that Mort kept on his tail. As the Rat King grumbles, the zoo animals quick repel the rats and send them cowering back into the sewers. Skipper rewards Mort by making him an honorary penguin. Mort takes this as a phrase seriously and knocks skipper to the ground with only one kick and says Skipper's catchphrase "You didn't see anything".