To ten-year-old Keeper, this moon is her chance to fix all that has gone wrong...and so much has gone wrong. But she knows who can make things right again: Meggie Marie, her mermaid mother who swam away when Keeper was just three. A blue moon calls the mermaids to gather at the sandbar, and that's exactly where she is headed -- in a small boat, in the middle of the night, with only her dog, BD (Best Dog), and a seagull named Captain.

When the riptide pulls at the boat, tugging her away from the shore and deep into the rough waters of the Gulf of Mexico, panic sets in, and the fairy tales that lured her out there go tumbling into the waves. Maybe the blue moon isn't magic and maybe the sandbar won't sparkle with mermaids and maybe -- Oh, no..."Maybe" is just too difficult to bear. Kathi Appelt follows up to her New York Times bestseller, The Underneath, with a tale that will pull right at your very core -- stronger than moon currents -- capturing the crash and echo of the waves and the dark magic of the ocean.