War has hovered around the kingdom of Scylla for generations ever since the original sirens left the mer collection generations ago after nearly drowning the human prince. Over the years, select mermaids from the royal bloodline have been trained as spies to work for the reigning kings and queens, keeping the collection safe from sirens and humans. Celena and her partner, Merrick, work covertly for the royals-not even her twin brother knows. When they discover the sirens have broken through the barriers the mer set up to keep the sirens out, Celena and her friends must race to the old kingdom of Metten to stop them from starting a war within their borders. When she's dragged to the surface, Celena realizes that the war above the waters is as deadly as the one below the waves-and sacrificing herself may be the only way to protect her family. The Siren Wars have only just begun.