Behold the orphan. Born into a world that is not a world. A digital being grown from a mind seed, a genderless cybernetic citizen in a vast network of probes, satellites, and servers knitting the Solar System into one scape, from the outer planets to the fiery surface of the Sun. Since the Introdus in the 21st century, humanity has reconfigured itself drastically. Most chose immortality, joining the polises to become conscious software.

When Enae's grandmaman passes away, Enae inherits something unexpected: a diplomatic assignment to track down a fugitive who has been missing for over 200 years. No one actually expects Enae to succeed; it's an empty assignment meant to keep hir occupied. But Enae has never had a true purpose—no one ever expected hir to do more than care for grandmaman—so sie is determined to accomplish this task to the best of her ability.

AD 3580. The Intersolar Commonwealth has spread through the galaxy to over a thousand star systems. It is a culture of rich diversity with a place for everyone. A powerful navy protects it from any hostile species that may lurk among the stars. For Commonwealth citizens, even death has been overcome.

This science fiction novel describes the epic voyage of the spacecraft Leonora Christine. From practically the very first minute, Tau Zero sets scientific realities in dramatic tension with the very real emotional and psychological states of the travelers, exploring the effect of time contraction due to traveling at near-light speed on the human psyche. This tension is a dynamic that Anderson explores with great success over the course of the novel, as 50 crewmembers settle in for the long journey together.

The year is 2380. The Intersolar Commonwealth, a sphere of stars some 400 light-years in diameter, contains more than 600 worlds, interconnected by a web of transport "tunnels" known as wormholes. At the farthest edge of the Commonwealth, astronomer Dudley Bose observes the impossible: Over 1,000 light-years away, a star...vanishes. It does not go supernova. It does not collapse into a black hole. It simply disappears.