Some family secrets don't stay hidden. Kelsey was like every other teenage girl until the day her world is turned upside down. She finds out after taking a dip in her best friend's new saltwater pool that she can turn into a mermaid. Once she confronts her mother she learns the truth, that her mother has kept their abilities a secret for fear of hurting those around them. But Kelsey insists on learning about where she comes from, even if her mother would rather ignore it all. They agree that she can visit her grandmother in Texas in order to understand what they are and where they come from. But it's not all just fins and saltwater. She learns there's a reason why people also call mermaids sirens, and that there's a dark side to the ability. One that caused her mother to turn away from being a mermaid for good. At her grandmother's, she learns of a whole underwater world that she never knew existed. Kelsey begins to learn who she is and what she's about as she meets new people. Including two boys that are looking to win her heart, one on land and the other at sea.