Through a mishap in Professor Bulfinch's laboratory, Danny accidentally creates an anti-gravity paint. The natural use, of course, is for a spaceship -- the paint can replace rockets to get the ship into space. Unfortunately, the spaceship is launched prematurely after Danny and Joe follow Professor Bulfinch and Dr. Grimes on a tour of the ship. A mechanical failure dooms the four to a one-way trip out of the Solar System -- unless they can repair the spaceship in time!