Wolf Wing by Tanith Lee

At last, Claidi and her beloved Argul are free to get married. But before they can start their life together, Claidi must face her past. They return to her birthplace, the House, to rescue the other slaves—and find that there has been a revolution, sparked by Claidi’s escape. Then the two are urgently summoned by Ironel Novendot of the Wolf Tower, who tells them that Ustareth is alive. Ustareth, the mother of Argul and Venn, the science-sorceress, who has perhaps manipulated each of them for their entire lives. Now she wants them all to visit her—but to what end?

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