Elysium: Mutant Year Zero RPG - Rules of Play says:
Mutant: Elysium is the third major expansion to the award-winning Mutant: Year Zero roleplaying game. This game tells the origin story of the enclave humans, seeing themselves as the last torchbearers of human civilization. The four Houses of Warburg, Fortescue, Morningstar and Kilgore struggle for power in the Elysium I enclave, oblivious to a rising power that threatens to end their reign forever. Mutant: Elysium can also be played as a stand-alone game.