Athena Crowley is an 11-year-old girl who lives at the Atlantis Resort in the Bahamas, where her father discovered the mythical Lost City for which it was named. Her life changes when an old turtle starts talking to her, and Athena realizes she can communicate with sea creatures. Determined to understand her roots, Athena takes a risky journey to the undersea kingdom of Atlantica, where mer-people rule, humans are slaves, and dangerous, thrilling surprises await her.