Almost a quarter of a million loyal Space Marines lost their lives on Isstvan V — the massacre lasted only a few hours, and the Iron Hands, the Raven Guard, and the Salamanders were killed by those whom they once called brothers. The disappearance of their primarch greatly affected them; Ra’stan and Usabius XVIII of the Legion left their surviving comrades behind. Their task: to find the remains of the great Vulkan…