When her older brother Thaddeus is mysteriously kidnapped by the Spellbinder, 11-year-old Lydia sets off to find him in the Misty Sea. Picked up by the crew of a flying ship, the Dolphin, Lydia becomes the apprentice of Ambrosia, a Stargazer. Ambrosia is trying to find other children who have disappeared, including her own son. Determined to solve the mystery, Lydia must learn astromagic and ready herself to confront the Spellbinder.