Michelle earns $221 selling lemonade on a very hot day in the fall, so she goes to the candy store with Kimmy Gibbler. However, they get sidetracked while passing by a petting zoo. Michelle comes home with a donkey, whom she names Shorty. (Conveniently, he just happened to also cost $221 - after she tells the man selling him how much she has.) The problem is, he can't be taken back to the petting zoo because, according to Kimmy, it is kind of a "traveling petting zoo", and that "they were packing up to go to Seattle". So Danny agrees to let Michelle keep him until morning; for the time being, he asks that Michelle feed and clean up after him. Michelle says she's fed and cleaned up after her hamster, but D.J. assures her that feeding and cleaning up after Shorty is going to be a much bigger responsibility than she thinks...much, much bigger.
While everyone is asleep, or at least trying to get so, he starts braying. By this time, it is almost midnight. It seems that he is quiet whenever Jesse sings the Three's Company theme song, so he does so to him all night in order to keep him quiet.
In the morning, Stephanie discovers that he chewed a chunk out of a map she made for geography class the previous day. D.J. has an allergic reaction to him, where she is all sniffly and her eyes are all puffy, and she has to wear sunglasses to protect herself from the dust. He then eats a hole through the painting of Danny's great-great-grandfather, General Cornwall Tanner. The neighbors, who thought about shooting Shorty, reject Danny's idea of a free donkey. Everyone likes Becky's idea of donating him to the local children's zoo. Unfortunately, that is not going to get Michelle any money to buy candy for everyone as she wanted, leaving her wallet empty. Michelle realizes that Shorty will always be in her heart.
Michelle's story with Shorty is similar to D.J.'s story with Rocket.