When her older brother Thaddeus is mysteriously kidnapped by the Mesmer, 11-year-old Lydia sets out to find him in the Sea of Mist. Taken in by the crew of the Dolphin, a flying ship, she becomes the apprentice of the astromagician Ambrosia. She is looking for other missing children, including her own son. Determined to solve this mystery, Lydia will have to learn astromagic and thus face the Mesmer.
