Setting out to exterminate the upstart Tau Empire before they become the threat, the Ultramarines under Captain Atheus discover that the xenos may be more of a menace than they originally believed…

It is the 41st millennium, and an upstart alien empire has emerged on the Eastern Fringe. After a few skirmishes to retake human worlds from these blue-skinned invaders, the time has come to strike against the so-called Tau Empire. At the forefront of the Damocles Crusade stand the Ultramarines, commanded by Captain Atheus, the Chapter’s Lord Executioner. With his loyal sergeants Numitor and Sicarius by his side, Atheus vows to exterminate the aliens… But the cunning xenos commanders, Farsight and Shadowsun, have other plans.

It's a look at an early encounter between the Tau and the Imperium, shown from both sides. See how both races view each other, through the eyes of some of their greatest heroes as they clash over the fate of a world. Plus, it's a rare chance to see Farsight when he was still loyal to the Ethereals and fighting alongside Shadowsun.