Once the brightest star of the Imperium and first among his brother Primarchs, Horus drew the Space Marine Legions into a bloody conflict the likes of which the galaxy had never seen. While their allies fight on numerous fronts, the XVI Legion lands on the knightly planet of Molech - the domain of the ruling House Devine, and one of the key bastions of the Imperial Army. The remaining troops loyal to the Emperor are preparing to meet the Warmaster, but what exactly will Horus use to attack such a protected planet, and what will he have to sacrifice to follow the dictates of his dark destiny?