Black Waters (Book 1 in the Songstress Trilogy)
Sixteen-year-old mermaid Abby Carson thought her secret was under control. But when she witnesses a murder off the coast of Cape Cod, everything changes. Hiding in the water is a must. Getting seen by Brian Baker, a boy from school, isn't. Neither is falling for him. Soon, Abby is pulled into a world of shades and monsters, and the only one she can hurt more than herself is the boy she loves.