A Sorcerer's Treason: Sarah ZettelBook I of Isavalta. 1899, Sand Island, Wisconsin: Bridget Lederle is a lighthouse keeper on this stormy, windswept shore of Lake Superior. One cold night she sees a boat foundering near the island's shoals, and rescues its lone occupant. The strangely dressed sailor tells her a fantastic tale, of Isavalta, a world where magic reigns, and where she is incredibly destined to play a key role in a power struggle between the Dowager Empress and her foes.