Martin Gibson is a famous science fiction author. He has written stories about the planet Mars, but has not actually been there. He travels with the crew of a spaceship to visit Mars.
On Mars, Gibson meets the people who manage the human settlement on Mars. They are working hard to make the colony as self-sufficient as possible (so that they don't have to import supplies from Earth)
Gibson joins a party of men exploring the surface of Mars. They discover a small group of kangaroo-like creatures, which had not been seen before. They are vegetarians, living on native plants.
Researchers try to cultivate these plants to increase the oxygen content of the Martian atmosphere, so that in a few hundred years, people can live without spacesuits.
Gibson discovers that Jimmy Spencer, one of the crew of the spaceship, is his son. Spencer has fallen in love with Irene Hadfield, who lives on Mars.
Gibson decides to stay on Mars, fascinated with the importance of the planet as a self-sufficient world.