On the medieval world of Sigmatus, two naive children, Dathan and Hycilla, become entangled in a plot to summon a powerful daemon in an attempt to protect a group of Chaos cultists from the oppressive forces of the planet's governor. With the Warp Storm that has isolated Sigmatus from the rest of the Imperium for two-hundred years abating. Imperial forces race to prevent the planet succumbing to the Dark Powers.