A Mermaid's Tale: Adventures of the Boy and the Magical Shell
Thirteen-year-old Justin has about had it with his sister and her friend. When he goes to the beach to blow off some steam, he comes across a shell necklace. The necklace ends up belonging to an underwater world full of mermaids and magic! When a British dolphin mistakes him for a merboy (because of the necklace) and takes him to a mermaid colony, a mergirl, Cora, befriends him and tries to get him back home before he is trapped in this underwater world forever!