In the third book of the legendary Revelation Space trilogy, the last remnants of humanity realize that forging an alliance with a greater and even more mysterious alien force may be their only chance for survival.

"A landmark in hard SF space opera." -Publishers Weekly

The Inhibitors were designed to eliminate any life form reaching a certain level of intelligence-and they've targeted Humanity. War veteran Clavain and a ragtag group of refugees have fled into hiding. Their leadership is faltering, and their situation is growing more desperate. But their little colony has just received an unexpected visitor: an avenging angel with the power to lead mankind to safety-or draw down its darkest enemy.

And as she leads them to an apparently insignificant moon light-years away, it begins to dawn on Clavain and his companions that to beat one enemy, it may be necessary to forge an alliance with something much worse ...