After a long and distinguished career defending the Imperium from its many enemies, Commissar Cain is enjoying a well-deserved retirement on Perlia, teaching in a schola progenium. But when a Black Crusade threatens the sector, all able-bodied citizens must rise to the defence, including Cain and his cadets. As the forces of Chaos overwhelm Perlia, can the wily commissar prove himself to be a real hero of the Imperium one last time?