Warhammer 40,000 storm of iron

On the nightmare battlefields of the Warhammer 40,000 universe, few foes spark more fear and dread than the Chaos Space Marines. Nurturing a hatred that is millennia-old, they attack without mercy, spreading terror and destruction in their wake. Now hell has come to Hydra Cordatus, for a massive force of terrifying Iron Warriors, brutal assault troops of Chaos, have invaded the planet and lain siege to its mighty imperial citadel. But what prize could possibly be worth so much savage bloodshed and destruction and how long can the defenders possibly hold out?