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