Merfolk - strong and resilient in the face of environmental threats and possessed of magical and telepathic powers - have long hidden themselves in the depths of the ocean, developing a rich world apart from walkers. The Aquademy, an advanced school of technomagic and undersea education, is one of their most prestigious institutions. When Marisa quits its magical halls, she is hoping for a calmer life than a future as a Sea Witch promises. Plagued by disturbing dreams about her deceased mother, Marisa returns home. But life back home proves to be anything but secure when merfolk begin to disappear and Marisa herself seems to be coming unglued. Her father doesn't approve of her erratic behavior or of her living alone under such dangerous conditions. She is forced to return to the Aquademy where she discovers that her oldest brother, Sail, is the latest victim in the series of disappearances. Counting on their strong telepathic connection to reunite them, Marisa defies authority and stages a ruse that helps her escape the heavily guarded Aquademy. She sets out on a journey that tests her resolve and taps into magical powers she has no idea she possesses. Meanwhile, Sail faces his own tribulations, kidnapped at sea on a ship called The Sea Witch. Together, the siblings learn of their connection to magic, to merfolk history, and to the dark secret of The Sea Witch.