After Detan retrieves the renowned engineer Nouli from the clutches of the empire, he returns to his aunt's city to find it under siege by Thratia's army. With Nouli's help, they turn back the tide - until imperial forces show up, prepared to hammer Thratia's army against the anvil of the city's walls. Worse yet, the imperial advance is aided by an elite force of deviant magic users. His aunt is forced to forge an uneasy alliance with Thratia to keep the city from falling back under imperial control - but Detan's wary. While Thratia and his aunt bring their forces to bear against the imperial threat, Detan puts his own plans into motion, scheming to ensure that when the final blow is dealt, Thratia and her army find themselves on the other side of the city's walls.