The book by popular American science fiction writers F. Paul and J. Williamson tells about exciting adventures in the underwater country of Marinia. The existence of an entire state on the ocean floor became possible thanks to the invention of the famous scientist Stuart Eden of a special material capable of withstanding the pressure of huge layers of water. In the novel “Underwater Expedition”, cadets of the Submarine Academy Bob Escove and Stuart Eden’s nephew Jim investigate the case of the scientist’s inheritance - uranium deposits on the bottom of the ocean trench.