Emily Windsnap is finally enjoying a swimmingly peaceful life on Allpoints Island, hanging out with her mermaid BFF, Shona, and her new friend Aaron (half-merperson like herself ). But their idyll is cut short when Emily learns that the Windsnaps and friends must return to their old home in Brightport, where construction projects are threatening a secret mermaid community under the sea. Neptune's mandate? No less than an interspecies intervention to bring merpeople and humans together, a task the imperious god feels the mixed Windsnap family is well suited for. There are just a few snags for Emily, however, like dealing with old nemeses Mandy and Mr. Beeston, figuring out her feelings toward Aaron, and untangling a high-suspense mystery related to a group of legendary lost sirens. Everyone's favorite half-mermaid is back with a splash in a sparkling adventure her fans will be eager to get their fins on.