Mickey is playing a game of catch with Pluto when Minnie drives by, reminding Mickey to meet her for dinner tonight. Mickey says he'll be there "unless they lock me up and throw away the keys." Mortimer overhears this and, while Mickey and Pluto aren't looking, snatches the baseball they're playing catch with. When Mickey comes looking for the baseball, Mortimer suggests to him that it landed in his house. When Mickey sees his baseball on the floor in Mortimer's house, Mortimer helps him climb in the window. Just as Mickey gets his hands on the baseball, Mortimer suddenly acts as though Mickey has broken into his house and then has Chief O'Hara, whom he has already called, come in and arrest Mickey.
In court, Mortimer tells the judge, Pete, that Mickey broke in to steal his baseball, and then shows "video evidence" of himself, poorly disguised as Mickey, stealing the baseball and insulting the judge. Offended at the false Mickey's remarks, Pete has the real Mickey thrown in jail. He uses his one phone call to call up Goofy ("Don't leave a message after the tone, 'cause this is me in person") and ask him to come bail him out. Goofy arrives soon (after having checked all the other jailhouses in town) to bring Mickey a piece of cake with an iron file hidden in it. The nearby police guard catches them in the act, though, but then proceeds to explain what one would need to cut the jail bars. Mickey then gets the guard to say that the easiest way for a prisoner to break out is to "knock me out and take the keys", and he even proceeds to demonstrate when Mickey asks him to.
Mickey rushes to the restaurant where Minnie is waiting for him, but Mortimer is heading there too. Mortimer makes it to the door before Mickey does, but before he can go inside, Chief O'Hara suddenly arrests him. As it turned out, they took another look at the baseball and saw that it had a "Property of Mickey Mouse" signature written on it. O'Hara gives the baseball back to Mickey and apologized for the mix-up before he drags Mortimer away while Mickey goes in to the restaurant to meet Minnie for dinner.
Back at the jail, the guard continues to teach Goify how to break out a prisoner (with tons of other guards already knocked out). Goofy finally gets how it goes and proceeds to knock the guard out.