Claire and Haley, two 13-year-old best friends, embark on the adventure of their lives when they discover a mermaid named Aquamarine in a swimming pool. Claire and Hailey are trying to come to terms with Hailey's impending departure: She's moving to Australia with her marine biologist mother after this last weekend of the summer. The beautiful, blue-haired, 18-year-old mermaid swam away from home just before her arranged marriage, in search of real love. If she can prove to her father that love is not a myth, he'll let her out of the underwater wedding, but he's only giving her three days. Aqua enlists the help of Claire and Haley, who are self-styled relationship experts. Aqua promises to grant Claire and Hailey the wish of their choice if they help her and the girls jump at the opportunity--because unless something magical happens, Hailey will be moving.