Through a mishap in Professor Bulfinch's laboratory, Danny accidentally creates an anti-gravity paint.

The spaceship is launched prematurely after Danny and Joe follow Professor Bullfinch and Dr. Grimes on a tour of the ship.

A mechanical failure dooms the four to a trip out of the Solar System unless they can repair the ship.

After his teacher congratulates Danny for his spaceflight, he gives her the punishment assignment on which he worked while on board, and she says she will keep it as a souvenir.

Floyd C. Gale wrote in Galaxy Science Fiction that the book "demonstrates a wonderfully brash humor ... let your 8-to-12-year-old find out the rest of the story for himself".