A man from Earth is mysteriously transported to Mars, where altered gravity and alien customs make him an unusually powerful combatant. He is taken by a nomadic green tribe, earns their trust, and learns the language and ways of the planet. The plot traces his repeated captures and escapes, his rescue of a noble captive with whom he forms an affectionate bond, and his involvement in the rivalries of city-states. Episodes range from arena contests and personal duels to raids on fortified cities and missions involving flying craft and atmospheric plants, culminating in wide-scale battles, shifting alliances, and the attempt to secure the captive's liberty and a tenuous peace.