Tidebound

She was never meant to be a hero. The sea had other plans. After a mutiny leaves her stranded on a deserted atoll, sixteen-year-old navigator's apprentice Mara Vega discovers two impossible things: a wounded mythical sea creature called a hippocampus, and a cryptic riddle-brand burned into her arm by her dying captain. When she bonds with the creature-a forbidden connection the empire has spent centuries trying to destroy-Mara becomes the most wanted fugitive on the ocean.
Hunted by a relentless commander and his armored war-shark, she must cross treacherous waters, face ancient guardians, and unlock the secret of a sunken treasure that could free the seas forever-or doom them to eternal chains. The tide is turning. And the deep remembers.