Arnold wants to know what happened to the heat from his cocoa. Ms. Frizzle thinks it is fitting to learn about heat in the land of ice and cold, so she takes the class to the Arctic. However, she accidentally drives the bus into the water, and the engine freezes. To make matters worse, the bus has been trapped on an ice flow with Phoebe, Ralphie, and Liz. The rest of the class will have to get to it and heat it up to escape.