As a penalty for fighting fellow classmates days before graduating from West Point, J.E.B. Stuart, George Armstrong Custer and four friends are assigned to the 2nd Cavalry, stationed at Fort Leavenworth. While there they aid in the capture and execution of the abolitionist, John Brown following the Battle of Harper’s Ferry.

In 2020, after the colonization of the moon, the spaceships Vega, Sirius and Capella are launched from Lunar Station 7. They are to explore Venus under the command of Professor Hartman, but an asteroid collides and explodes Capella. The leader ship Vega stays orbiting and sends the astronauts Kern and Sherman with the robot John to the surface of Venus, but they have problems with communication with Dr. Marsha Evans in Vega.