The Heresy came to Calth without warning. In just a few hours of betrayal and bloodshed, the proud warriors of the XIIIth Legion – Guilliman’s own Ultramarines – were laid low by the treachery of their erstwhile brothers of the XVIIth. Now, as the planet is scoured by solar flares from the wounded Veridian star, the survivors must take the fight to the remaining Word Bearers and their foul allies, or face damnation in the gloomy arcology shelters beneath the planet’s surface. In this all-new collection of stories by authors including Dan Abnett, Aaron Demsbki-Bowden and Rob Sanders, witness the untold tales of the Underworld War. In the novella-length ‘Calth That Was’, Graham McNeill highlights the fateful encounter that will alter the destiny of Captain Ventanus and shape the face of the Ultramarines Chapter for ten thousand years to come. The battle for Calth is far from over.