It's Broadcast Day in Ms. Frizzle's class. It was Ralphie's job to find an exciting story that the class could cover for the news. But Ralphie is at home sick. That won't stop Ms. Frizzle. She thinks Ralphie's cold is the perfect topic for the class's news program.
All abroad the Magic School Bus as the gang travels through Ralphie's bloodstream and finds out how germs made him sick - and how his body can make him well again.