Another blazing far-future saga from Schroeder (Ventus, 2000, etc.). In this universe, brown dwarfs—bodies midway between giant planets and small suns, whose feeble glow results from gravitational contraction, not nuclear fusion—abound. Humans, colonizing the galaxy at sub-light speeds, occupied many of these `halo worlds` and established the Cycler Compact, trading among the colonies in sub-light spaceships called cyclers. But with the invention of faster-than-light ships, the lit worlds—they have fusion suns massive enough to ignite the FTL drive—established the predatory Rights Economy, abandoning the halo worlds to a spiral of decline. Young Rue Cassels, fleeing her abusive, ignorant brother Jentry, arrives at the halo world Erythrion just in time to detect what turns out to be not merely a derelict cycler but an alien vessel. She's forced to share possession of the ship with the Rights Economy's Admiral Crisler (he's looking for weapons to help the R.E.'s struggle against their own increasingly successful rebels) and alien experts Laurent Herat and Michael Bequith. Herat's researches show that civilizations always, in the long run, fragment into warring factions and become extinct. Only two species bucked the trend: the Chicxulub, who 65 million years ago destroyed all competing lifeforms throughout the galaxy; and the Lasa, who may have pioneered a way to survive and prosper in the environment offered by the halo worlds. So everybody has cogent reasons for discovering the origin of the alien vessel and plumbing its secrets.
Once again, the plot—of which the foregoing is barely a hint—arises organically from the backdrop and characters: thoughtful, well-informed, insightful work, with a sharp yet subtle political subcontext, catapulting Schroeder into SF's front rank.