Sylvester Cat scoffs at his son's idea that a pipe like that of The Pied Piper of Hamelin could lure mice into their home to catch. But when Junior tries it and Hippety Hopper, the baby kangaroo, comes along, Sylvester believes in the power of the pipe and that Hippety is a giant mouse.
Sylvester Cat accepts a position as mouse-catcher on a ship, and his son, Junior, accompanies him. They encounter baby kangaroo Hippety Hopper being shipped from Australia and, as usual, mistake Hippety for a giant mouse.
On their way to Night School, Casper the Friendly Ghost and his pal, Spooky Ghost, pass a zoo, and Spooky has a good time scaring the animals until Casper, posing as the ghost of the scared denizens of the zoo, scares Spooky.
