It is 41st Millennium, and the only force that stands between humanity and alien hordes are the Space Marines. Genetically enhanced, clad in power armour and knowing no fear they are the angels of death. And the greatest of them are the Ultramarines. But when a select squad of scarred veterans and raw recruits responds to a distant planet's distress beacon, they'll discover that a horrific evil has been unleashed. And amidst a living nightmare of chaos, carnage and daemonic fury, these steel battle-brothers must now survive the ultimate enemy: Themselves.