The Alden children are on vacation at an aquarium in Florida. The Boxcar Children will feed the penguins, swim with dolphins, and come face-to-face with a great white shark! The shark draws crowds and thrills the park's visitors. But the Aldens soon discover that the shark is in danger--someone at the park wants it gone. The Boxcar Children are determined to fish out the crook before it's too late for the shark.