[2] Based on the 1844 fairy tale of the same name by Hans Christian Andersen, The Snow Queen takes place on a mostly oceanic planet called Tiamat.

It orbits a double-star system impacted by a third stellar companion, the Summer Star, that destabilizes the "Black Gate" every 150 years.

The residents of Tiamat are split into two clans: "Winters", who advocate technological progress and trade with offworlders, and "Summers", who depend on their folk traditions and rigid social distinctions for survival.

The Hegemony's interest in Tiamat lies in mers, a species of sea-dwelling creatures whose blood contains a smartmatter virus that halts the aging process.

Arienrhod, the Snow Queen, has secretly implanted several Summer women with clones of herself, in the hopes of extending her rule past her ritual execution at the end of Winter.

Hegemony law prevents any native Tiamatian from returning after leaving the planet, fearing that travelers would realize how Tiamat is being exploited and use this knowledge to foment rebellion.

Arienrhod devises a backup plan; she will unleash a plague at the Change which will kill most Summers and spare most Winters, allowing Tiamat to continue its technological growth before the Hegemony returns.

Moon is taken to the capital planet, Kharemough, and discovers that the Winters' prejudice against sibyls is a political tool used by the Hegemony to preserve its control of technology on Tiamat.

Sibyls are highly respected throughout the other planets of the Hegemony; only on Tiamat, due to a careful reinforcement of superstitions during the reign of Winter, are they considered dangerous and mentally unstable.

After a crash landing and short sojourn as a captive of Winter outlaws, Moon returns to Carbuncle and confronts Arienrhod.

Later reviewers have admired the complex world-building Vinge created with the planet of Tiamat and the Hegemony calling it a “carefully crafted universe”[4] and “impeccable and expansive”.