Patricia A. McKillip 
Tower at Stony Wood [EPUB ebook] 

During the wedding festivities of his king, Cyan Dag, a knight of Gloinmere, is sought out by a mysterious bard and told a terrifying tale: that the king has married a false queen — a lie cloaked in ancient and powerful sorcery. Spurred on by his steadfast honour and loyalty, Cyan departs on a dangerous quest to rescue the real queen from her tower prison — to prevent war, and to awaken magic in a land that has lost its way …