A giant spaceship has been built in a nearby orbit, and an Earth inspector arrives aboard the station with new orders: Merritt Sr. is being promoted to general and will command the new spaceship, now being sent to Mars instead of the Moon. As General Merritt considers his crew of three enlisted men and one officer, his close friend, Sgt. Mahoney volunteers. The general turns him down for being 20 years too old. Hearing that Mars is the new destination, Barney Merritt volunteers to be the second officer.