Julian 5th sets out aboard the spacecraft Barsoom on a pioneering voyage but is drawn to the Moon, where he discovers the vast inhabited inner world of Va-nah and is captured with his companion Orthis by the savage four-legged Va-gas. There he meets Nah-ee-lah, princess of the lunar city of Laythe, and after enduring captivity together they escape during a violent storm, cross dangerous volcanic country, and gradually develop a deep bond as they struggle toward her homeland. Their journey brings them into conflict with the warlike Kalkars, and Julian is finally captured, drawing him still deeper into the political and military dangers of the Moon.
