Absolution Gap

They are ancient killing machines, designed to locate and destroy any life form reaching a certain level of intelligence. Now, stirred from eons of sleep, the Inhibitors have descended on their latest target: Humanity." "The first wave of Inhibitors has sent war veteran Clavain and a ragtag group of refugees 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." 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.

Synopsis from Open Library.