The Battle of Tallarn grinds on to its climactic end, but what secret purpose drives the Iron Warriors to commit such mindless atrocities? The answer lies buried deep beneath the planet’s surface...

As one of the many staging grounds for the forces serving in the Great Crusade, the verdant world of Tallarn has long served as a transfer point for the personnel and war machines of the Imperial Army. Now, destroyed by a deadly virus-bomb attack launched by the fleet of the vengeful primarch Perturabo, the entire world is reduced to a toxic wasteland where the survivors must fight to defend what little remains of their home. As the battle for Tallarn rages between the traitor Iron Warriors Legion and the Imperial Army, a carpet of armour covers the surface of the toxic planet: Dreadnoughts versus tanks versus Titans. But what secret purpose drives the Iron Warriors onwards to war?