It's a former Tau world, overrrun with Orks of the Angry Eyez Klan. Hunter Cadre D'yanoi has been assigned to retake the world in the name of the Tau Empire. Meanwhile, the Orks uncovered an ancient artifact, and in their stumbling, activated it, sending a signal across the Warp. The Black Legion and World Eaters traitor Legions responded to the signal, speeding onwards in insane, mindwrenching glory for the Dark Gods. The Imperium of Man detected this signal, and sent the Imperial Fists and Ultramarines Chapters to the planet, alongside the 51st "Blasted Cavalry" and 52nd "Forgefane Fighters" Imperial Guardsmen regiments, as well as the Order of the Sacred Tears, an Adepta Sororitas group. The nature of the artifact is only known the Orks at this point, even though they do not understand it.