In the year 2338, humanity is united in the Solar Alliance, with representatives from Earth, Mars, Venus and the larger satellites such as Titan, Ganymede and Luna. Peace is maintained by the Solar Guard, whose officers are taken from the Space Academy.
Tom Corbett enrolls as a cadet in the Academy, and is teamed up with two other cadets. The Space Academy’s tradition is that cadets work as a threesome, and are judged by how well they do as a unit. Tom gets along very well with the big Venusian cade Astro, but both he and Astro have trouble with Roger Manning. As time passes, they realize that there is some dark secret in Manning’s past which he refuses to share with anyone.
Then, while on a training mission, they are dispatched to rescue a disabled spaceship. They attempt to bring the ship to a safe harbor on Mars after the crew is evacuated, but the damage is too extensive and they crash-land. Now the three cadets will have to learn to work together—or they will all die together on the barren sands of the red planet.