Waterfire Saga, Book Four: Sea Spell: Deep Blue Novel, A

At the end of Dark Tide, Book 3 in the Waterfire Saga, Astrid leaves her mermaid friends to confront her ancestor, Orfeo, the evil force behind the rise of the monster Abbadon. Orfeo possesses one of the six talismans that the merls need in order to keep the monster locked up forever. But without the ability to songcast, how will Astrid be able to defeat the most powerful mage in history? Meanwhile, Serafina and her Black Fins train goblin troops for battle against her uncle Vallerio's death riders. Will Sera ever see her beloved home--and her beloved Mahdi--again, or will the Volneros take over the mer realms while Orfeo takes on the gods themselves? Nothing less than the fate of the underwater world is at stake in this breathtaking finale.