One day, when Cassandra and her mother were walking through a forest to go back home, Cassandra's father evidently shows up, and murders Cassandra's mother. He killed her by burning her with fire that came out of his own hands.
Cassandra is then sent to live with her grandmother in Greece. So her brother came to pick her up, and they both flew across the country. But in the plane ride, Cassandra learns some rather disturbing things.
She learns that she is a mermaid with mystical powers. Her father was sent to retrieve a necklace that her mother was wearing which could mean world domination. Dracia, an evil mermaid, wants the necklace that used to be Cassandra's mother's, but which Cassandra then kept.
It is Cassandra's duty to protect the necklace from getting into their hands at all costs.
So she lives in an underwater city named Hudor. She learns about the ways of a mermaid, and even more about the war period they have been going through.
But what happens when Dracia evidently retrieves the necklace? Will Cassandra be able to get it back before the time runs out? Or will she end in defeat, and will the end of the seas be on her head?
You must read to find out!