The Chaos Space Marines of the Iron Warriors Legion have long been renowned as the masters of siege warfare, able to inflict devastating firepower and unimaginable cruelty upon their foes. On the world of Castellax, twisted Warsmith Andraaz builds his own empire even as a system-crushing ork Waaagh approaches, and drives his own slaves ever harder to meet their production quotas to supply material for the Legion's many warbands.