It's beach day, and the whole class is excited. Everyone except Arnold and Keesha, that is. They forgot their report on two beach things that go together. All Arnold and Keesha have is a tunafish sandwich and some smelly green pond scum. What could those two things possibly have in common? "The best way to learn about something is to jump right in," Ms. Frizzle announces. A second later the bus dives right into the ocean! Come on an underwater adventure and learn about food chains.