Hippety Hopper, a baby kangaroo, escapes from the zoo and causes a number of problems around town. Meanwhile, Sylvester Junior wants to learn to catch mice, but Sylvester can't teach him because there are no mice in the house. Sylvester scoffs at Junior's idea of making a pipe like the one in his storybook, The Pied Piper of Hamelin. Junior carves one anyway, but is unsure how many holes to give it. He makes four holes, but when he plays it a pig comes grunting to him. He makes another hole in the pipe and this time it attracts a cow. When he adds a sixth hole, Hippety appears beside him.
Junior wakes his father from a nap to tell him the pipe works but Sylvester doesn't believe him. He tries it for himself and sure enough, Hippety appears. Thinking that Hippety is a giant mouse, Sylvester agrees to teach Junior how to catch him. Hippety knocks the cat through a wall, then pulls him back out. Sylvester tries to wrestle the "mouse," who takes him for a ride through the barnyard. When a truck from the zoo arrives to pick up Hippety, Junior realizes it wasn't a mouse and starts to carve a seventh hole in his pipe. Sylvester angrily stops him and says for little mice you need a little pipe. He breaks Junior's pipe in half and begins to blow, but is immediately attacked by a pack of bulldogs.
When this cartoon aired on ABC's The Bugs Bunny and Tweety Show, the sequence of Hippety Hopper escaping from the zoo was cut to remove Hippety Hopper jumping on a nurse's backside and the woman beating a man with an umbrella because she thinks he touched her inappropriately.
- This is the only time that Ben Washam ever animated for the Robert McKimson Unit.