The Siege of Terra looms, and the fate of the galaxy balances on a razor’s edge. Roboute Guilliman leads the immense fleet of the Ultramarines in a race towards the Throneworld, and such is the power he commands that he could turn the tide of the war in the loyalists’ favour. As determined as Guilliman is to reach Terra, Horus is as resolute in delaying his brother primarch until it is too late. Guilliman’s path through the Ruinstorm crosses through the Charchera system, and here Warsmith Khrossus and a lone company of Iron Warriors have been given a fateful mission. At all costs, they must hold back the Ultramarines. Guilliman foresees the coming ambush, but he has no choice but to plunge into it, and so begins a desperate struggle where the passage of every second could mark the difference between survival or extinction for the Imperium.