Almost three-quarters of a million miles around, Hegira has, against all the laws of physics, Earth-normal gravity; its different races have a common history: all the accumulated knowledge of the First-born, graven on giant Obelisks that rise up out of sight to the sky, beyond mankind's powers to reach and read. But as knowledge advances, so the enigmas of Hegira's nature become grew steadily more impossible to explain or to understand. The ill-assorted trio who embark on their personal quests know little of their planet's oddities and care less . . . until Hegira's changeless mysteries begin to alter; until the first great Obelisk tumbles.