When Nessa's dad dies, the last thing she's expecting is to lose everything else too. But when her hair suddenly turns electric red, and her estranged grandma turns up on her doorstep ready to haul her off to an isolated island, that's exactly what happens. In one day, Nessa loses her mother, her friends, and her life. Nessa discovers a new world at an international school for Neptunians, magical creatures blessed by the sea. Nessa learns that she's a sea-witch, and destiny has finally come to claim her.

Nessa's classmates are anything but normal, and magic flows through the veins of all who attend there. Selkies, mermaids, pirates, sea nymphs, and sirens abound in this tale about friendship, romance, and adventure. Nessa's life is about to be turned upside down, but there's someone out there who would prefer her dead. Will Nessa survive her first year as a sea-witch, or will the currents drag her down to her watery grave?