Late one night (in the world of the future), a giant cargo hovership makes an emergency landing somewhere in the middle of the United States and an enterprising teenager named Johnny Clinton stows away on it. In the space of only a few hours the craft crashes into the Pacific Ocean. The crew ("even the ship's cat") is offloaded onto lifeboats, leaving Johnny (who, as a stowaway, they did not know was on board) adrift in the flotsam from the hovercraft. His life is saved by the "People of the Sea"—dolphins. A school of these fantastic creatures guides him to an island on Australia's Great Barrier Reef. Johnny becomes involved with the work of a strange and fascinating research community where a brilliant professor (Prof Kazan) tries to communicate with dolphins. Johnny learns skindiving and survives a typhoon—only to risk his life again, immediately afterwards, to get medical help for the people on the island.