Siren Phillips has lived her life thinking she's an ordinary girl, in an ordinary town. On the eve of her twelfth birthday, however, she learns that she is far from ordinary. Destined to turn into a Mermaid at the age of twelve, Siren must struggle with her new reality, saying good bye to her mother and friends, while she transitions into the water.

To make matters worse, a group of Hunters are after her, trying to catch her. She soon becomes friends with Adam Wilts, a new boy at school, who she turns to for help. He agrees to help her, but finds himself caught in the middle, when it's his own father who is after Siren.

When Siren's mother is taken, the town must rally behind her, and help her make a peaceful transition into the water, before the hunters can find out where she is.