The novel is set in an undefined distant future (although it is implied to exist roughly 5000 years from now), in which there is a galactic empire spanning eighty worlds, amongst other human civilizations. The empire is ruled by the Risen Emperor, who has discovered the secret of immortality through means of a symbiont (spelled "symbiant" in the novel). Immortality is conferred on favored Imperial citizens, who, after their death, become 'grays', living in a zombie-like state and making pilgrimages in honor of the Emperor. To create balance, the living citizens of the Empire are represented by an elected Imperial Senate, and by elected governments on each world. Faster than light travel is impossible (although FTL communication via quantum entanglement is used), and the result of more mundane interstellar travel between the eighty worlds of the empire results in relativistic effects due to the high speeds involved; as such, the ages of space travelers become out of sync with those of their friends and family, an effect known as the "Time Thief". Other groups in the Empire, such as the Imperial Senate, are also subject to the "Time Thief" due to the use of cryogenic freezing. The Empire, protected by the Imperial Navy, is at war with a cult of fanatical cyborgs known as the Rix, who worship compound artificial intelligences and seek to spread such intelligences throughout the galaxy.
The central characters are Captain Laurent Zai of the Imperial Navy, and Senator Nara Oxham, a member of the Secularist Party, which opposes worship of the Emperor and the use of the symbiont to create immortality. Despite their political differences, the two become lovers. Zai is sent away to fight the Rix; due to the death of the Emperor's sister at the hands of the Rix, Zai is expected to commit ritual suicide to mark his failure, but chooses not to do so. Senator Oxham, appointed to the Emperor's War Council, opposes unpalatable war plans that would lead to the sacrifice of billions of Imperial citizens.