Betty Boop and Junior are excited when they look outside the apartment window and see a car heralding the carnival. "Today only," says the sign painted on the side. "And also all week!" Betty and Junior sing about the good time they're going to have at the carnival, but the moment they step outside, a thunderstorm begins and spoils their chance at some outdoor fun. Luckily, Prof. Grampy, who also lives in the building, hears Junior's temper tantrum and puts on his thinking cap. Moments later, the light bulb on the cap goes off, and Grampy has it! With his usual knack for on-the-spot inventions, he creates carnival games and carnival rides out of everyday objects, such as a seltzer bottle, a washtub, a trashcan, a table top and so on. The best is yet to come when Grampy turns the fire escapes around the building into a roller coaster.