Goodbye Mr. Fish
Sitting at the table in Mario Brothers Plumbing, Mario is eating some bread when the doorbell rings. Luigi sarcastically comments to Mario that nothing should disturb his eating, then climbs up to the door to open it. Standing on the other side is their elderly friend Mrs. Periwinkle, whom Luigi welcomes into the apartment. Mrs. Periwinkle is holding a fishbowl containing Kenneth, her goldfish. Mrs. Periwinkle asks Luigi if he can look after Kenneth for a few hours, but Luigi remarks that he doesn't know much about fish.
Leading Mrs. Periwinkle down the stairs, Luigi suggests to her that if she loves Kenneth so much, that she should just take him with her. Mrs. Periwinkle points out that she's going horseback riding, which she then claims Kenneth has a mortal fear of. Arriving at the table, Mrs. Periwinkle asks Mario if he'd be willing to look after Kenneth, which he agrees to without any real thought. Mrs. Periwinkle tells Mario that Kenneth is like the son she never had to her, except for the fact that he has gills and a tail, signifying his importance. Mrs. Periwinkle says goodbye to Kenneth, tells Mario to deny him if he asks for a piggyback ride, and leaves.
Luigi asks Mario why he agreed to look after Kenneth, and Mario responds that he did so because Mrs. Periwinkle wanted him to. Luigi then asks Mario if he would jump off the Brooklyn Bridge if Mrs. Periwinkle asked him to, and Mario points out that he could just wear his nose plugs. As Luigi walks off, Mario starts talking to Kenneth, telling him that he can't have a piggyback ride. Getting the idea that Kenneth is hungry, he nearly feeds him a meatball, but Luigi interferes and warns Mario that he shouldn't. Mario states that it would be easier to digest than a sausage, and drops the meatball into Kenneth's bowl.
Later, Mario and Luigi are staring into Kenneth's bowl, looking at the now-deceased fish floating in the water. Mario asks Luigi what he should say to Mrs. Periwinkle, but Luigi tells Mario to forget about her and asks what he should do about fish. Mario asks Luigi a second time, and Luigi suggests that he should tell her he warned Kenneth not to float on his back. Picking up Kenneth, Mario asks how he should tell Mrs. Periwinkle that she's no longer the owner of a goldfish, but instead a gold ball, and drops Kenneth.
Luigi then comes up with an idea: replacing Kenneth with a stand-in goldfish. Mario decides that they should turn to the Ratigator for help, and walk over to a grating. As Mario opens the grating, he asks the Ratigator if he's seen any goldfish in the sewer, and the Ratigator sticks his head out holding a large trout in his jaws. As Mario grabs the trout, Luigi remarks that it's not even human, and Mario states that he's doomed. The Ratigator growls at Mario's rejection of the trout, and Mario tells him he was aware that it was short notice. As Luigi and Mario ponder on the fact that they don't know what to do, the doorbell rings, and Mrs. Periwinkle announces her return from behind the door. Mario and Luigi start to panic, and Mario hides under the table while Luigi tosses the trout back to the Ratigator, telling him to get rid of it.
After Mrs. Periwinkle enters the basement, she asks Luigi where Kenneth is. Luigi tells her that he isn't around, and when Mrs. Periwinkles questions where Kenneth really is, he remarks that Kenneth swam away. Mrs. Periwinkle argues that Kenneth would never leave home, stating that he has three squares a day, a roof over his fin, and all the H2O he can drink. Luigi then gives up and confesses that something happened when Mario fed Kenneth his lunch, and tells Mario to get up from under the table. As Mario tries to approach Mrs. Periwinkle, she yells at him, asking if something has happened to Kenneth.
Before Mario can answer, he hears the Ratigator growling from the grate. Mario then tells Mrs. Periwinkle that Kenneth missed her; he goes over to the Ratigator, picks up Kenneth's bowl (which now has a new goldfish in it), and hands it to Mrs. Periwinkle. Mrs. Periwinkle is thrilled to have Kenneth back, and tells him that she'll give him a warm bath when they get home. Mrs. Periwinkle offers to pay Mario for looking after Kenneth, but he denies her offer, telling her that looking after Kenneth was his treat. Touched by Mario's generosity, Mrs. Periwinkle tells him that she'll tell all her friends to call him if they even need a fishsitter. As Mrs. Periwinkle leaves, Luigi starts blurting out the new fish-sitting rates that he and Mario are going to start using.