The Imperium of Man has many enemies among the stars, but none are reviled so much as the alien. Dangerous races seek to destroy humanity wherever they turn –the brutish orks, the ravening hordes of the tyranid, the unrelenting necrons and the mysterious forces of the tau and the eldar. Across the universe, humanity and their defenders, the Space Marines, seek to eradicate these xenos threats. Yet all they can hope for is another day of survival – for to stand against the alien is to enter an unending war...