The Reclamation

Through ONI's manipulation, the UNSC stumbles upon a Mass Relay and is dragged into a new war. They'll discover the battered races of the Citadel, the political intrigue of its factions, and a second group of humans governed by the Systems Alliance, divided by Cerberus, and lead by Commander Shepard. Yet no one can stop what is to come: the Reclamation, and the death of the galaxy.