On Isstvan V, the Retribution Fleet sought to bring Horus to account for the atrocities he had already committed against the Imperium. Unbeknownst to them, the roots of corruption ran deeper than any had yet dared to imagine. On the black sands of the Urgall Depression, brother opened fire on brother as the Horus Heresy began in earnest. It would come to be known as the Dropsite Massacre, and some Legions would never recover.
This narrative gaming supplement for Warhammer: The Horus Heresy digs deep into the conflict on Isstvan V, when the civil war that went on to engulf the galaxy
