The Well of Lethe. The Echo Plague, #1

Korvus is a Corrector, an agent of the machine god that rules humanity. Armed with a weapon that fires black holes and a faith forged in the fires of his own fallen world, he descends into the deepest prison in the galaxy to eliminate a rogue AI. His mission is to Correct the corruption-but he finds more than a heretical machine. The Well of Lethe is already rotting from the inside. The station is riddled with a horrifying biological plague, a parasite that creates perfect copies of its victims-and can fool the Communion's most sacred security systems.
Cut off from support and hunted by monsters that look just like humans, Korvus's only ally is the target: Verity, a sentient robot who preaches her own forgotten faith, may be the only being in the station he can trust. To survive, he must fight his way through a station where every shadow could be a friend, and every friend could be a monster waiting to strike. Failure doesn't just mean death. It means being consumed, copied, and becoming a weapon for an enemy that threatens to extinguish the light of humanity from the galaxy.
For the Echo Plague is coming, and it is armed with the one thing that can bring an empire of truth to its knees: the perfect lie.