This is a great book. Alice Hoffman is a amazing author. Yes, the movie was based on this book.
Hailey and Claire are spending their last summer together. After summer, Claire will move to Florida with her grandparents. This summer, they encounter a mermaid in the beach club's pool. Her name is Aquamarine and she is beautiful. But if she doesn't go back to the ocean anytime soon she will turn to dust. So Hailey and Claire try to convince her to go back to the ocean. But Aquamarine is very stubborn. She refuses to go back until she falls in love with someone. Then she sees Ray, a guy who works at the club and reads alot. She decides she wants him and convinces Hailey and Claire to set up a date with Ray and Aquamarine. So Aquamarine talks and sees Ray for one special night, but after a few hours, she starts to turn into dust so Hailey and Claire bring her back into the ocean before it's too late.
Then Aquamarine leaves and says goodbye.
But she leaves two shells.
I recommend this book very much.