A million years from now, the galaxy is divided between the vast, cooperative meta-civilisation known as the Amalgam, and the silent occupiers of the galactic core known as the Aloof. The Aloof have long rejected all attempts by the Amalgam to enter their territory, but have permitted travellers to take a perilous ride as unencrypted data in their communications network, providing a short-cut across the galaxy's central bulge.
When Rakesh encounters a traveller, Lahl, who claims she was woken by the Aloof on such a journey and shown a meteor full of traces of DNA, he accepts her challenge to try to find the uncharted world deep in the Aloof's territory from which the meteor originated.
Roi and Zak live inside the Splinter, a world of rock that swims in a sea of light they call the Incandescence. Living on the margins of a rigidly organised society, they seek to decipher the subtle clues that can reveal the true nature of the Splinter. In fact, the Splinter is orbiting a black hole, which is about to capture a neighbouring star, wreaking havoc. As the signs of danger grow, Roi, Zak, and a growing band of recruits struggle to understand and take control of their fate. Meanwhile, Rakesh is gradually uncovering their remote history, and his search for the lost DNA world ultimately leads him to a civilisation trapped in cultural stagnation, and startling revelations about the true nature and motives of the Aloof.
Hugo-winner Egan (Schild s Ladder), champion of ultra-hard SF, devotes most of this slim novel to the efforts of the Arkmakers, who live in a neutron star s accretion disk at the center of the galaxy, to develop orbital physics from first principles and save the artificial world created by their more sophisticated ancestors. Meanwhile, Rakesh, a more or less human member of a distant posthuman society, sets off on an unrelated quest to find the Arkmakers and is soon trying to save them from their current danger. Whole chapters are devoted to physics problems and include a variety of diagrams and cited sources. Egan s briefly sketched characters and cultures are interesting, but this one is all about the science and won t have much interest for those without at least some understanding of celestial mechanics.