"I challenge you to a duel of desert islands!" Dr. Grimes cries, when Professor Bulfinch accuses him of not being practical. Grimes plans to go ashore on an uninhabited desert island, and the professor on another. After a month they will see who has survived the best!
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!