On the class' first "normal" field trip to the zoo, they wonder how the animals could live in the city. Ms. Frizzle then turns them into various city animals (Tim, Arnold, and Phoebe into foxes; Ralphie, Wanda, and Keesha into opossums; Dorothy Ann and Carlos into peregrine falcons, and herself into a raccoon), but the bus mistakes itself for a bear, and with Liz inside, leaves them. Worse, the city authorities are after it, thinking that it is a lost animal needing to return home. Will the class get to it in time, or will they be animals forever?