A field trip to a mysterious island quickly turns into an adventure when Emily Windsnap and Aaron discover a secret lookout point from which they spot a ghostly ship that no one else seems to be able to see. The ship appears and disappears only at certain times of day--growing fainter each time. Searching for answers only leads to more questions until Emily and her friends confront the island's keeper, uncovering the incredible story of a ship caught between land and sea, day and night . . . life and death. Only Emily, with her ability to transform from mermaid to human, can enter Atlantis to try to bring the ship's passengers back before the portal is closed forever. Emily knows that if she fails, not only will the passengers never see their loved ones again, but Emily won't be able to return either. Will she be able to resist the allure of Atlantis and return home before it's too late?