A scuba-diving vacation in Australia turns serious when Miss Mallard and Willard discover that the Great Barrier Reef is being destroyed. But how? Why? And by who? These questions lead them on a search, literally under the sea, where Dr. Decoy, bent on world domination, has built an incredible underwater city. Miss Mallard, Willard, and the undersea explorer Jacques Canard throw a wrench into Dr. Decoy's plans and save the reefs of the world.