Jailhouse Rock Happy Days : Season 3 Episode 7

Because the high school was vandalized, Officer Kirk imposes a curfew. Richie suggests that they demonstrate against the curfew, get arrested, and fight it in the courts. While Richie, Potsie, and Ralph are in the restroom at Arnold's discussing their plans, the lights go out, and they discover they are locked inside after Arnold closes up for the night.