Mankind pisses off everybody. No. Seriously. In 2753, Mankind makes a colony on a small planet orbiting Proxima Centauri. On that planet, they come across a strangely humanlike species called the Vin. The human colonists become appalled upon discovering that another species, the Eth, have been farming the Vin for food. The ensuing war ends with the Eth deliberately destroying the planet's biosphere.
Meanwhile, far across the galaxy, the Magisterium watches the violence from afar. Their horror at the goings on is compounded by the realization that the aliens they're observing, who call themselves humans, had not been created by their gods. This leads them to wage holy war across the cosmos.
At the center of the galaxy exists an entity, created from the minds of the trillions of organisms it infests. As it curiously spreads its influence beyond the core, with desires of infection and control, it comes across a curious little species who hurt it very, very bad.
Mankind is in for a rough time.