Happy Days S03E15 - Dance Contest

Marion wants to join a dance contest but Howard and the kids think it's ridiculous. But she decides to enter with Fonzie and they spend their free time practicing. When she acts strangely because she's keeping it a secret from everybody, Howard wonders what's going on. And when Arnold who knows about it let's it slip that Marion is seeing someone else, Howard follows her. And when he sees her with Fonzie he loses it.