Synopsis: From the front flap of the Gregg Press edition: "Is sabotage going to wreck the test flight of the first anti-gravity space ship? Are all the secrets of Project Agrav on the satellite Jupiter Nine being sent to Sirius, Earth's powerful and ruthless enemy? And if so, which of a handful of men on Jupiter Nine is responsible for passing on the information? Or do the Sirians have a form of telepathy so strong it could literally pick brains? Earth's Council of Science needs the answers to these questions in a hurry. So Lucky Starr, youngest Council Member, and his side-kick Bigman Jones set off on one of their most hazardous and exciting investigations. A weird fight in the anti-gravity corridors of Jupiter Nine, a near drowning in a river of ammonia; and the terrifying first flight of the Agrave ship that nearly ends in disaster are a few of the adventures that Lucky and Bigman encounter. And the trail ends in the discovery of a saboteur so fantastic that the reader will be kept guessing right up to the book's thrilling climax."