In the coastal town of Crestwood, 16-year-old Mira Thompkins has always dreamed of becoming an oceanographer. She spends her days collecting shells and studying the ocean's mysteries. Everything changes when she discovers an ancient magical seashell buried in the sand—one that grants her the ability to communicate with Nereus, the legendary sea guardian. When Mira's power awakens, Lucas Hart, Crestwood High's charismatic top surfer, finds her and reveals he too carries a secret connected to the