"Astrid must confront her ancestor, Orfeo, the evil force behind the rise of the monster Abbadon, while Sera and her Black Fins train goblin troops for battle against her uncle Vallerio's death riders"--

A beautiful sea princess, longing to be human, trades her mermaid's tail for legs, hoping to win the heart of the prince she loves.

When her young friend, Laurel, mysteriously goes missing, Ariel reads Laurel's diary entry about a secret new friend and is accompanied by Sebastian, Flounder, and Scuttle while following clues.

"The final Guardians Trilogy novel from the #1 New York Times bestselling author of Bay of Sighs and Stars of Fortune. As the hunt for the Star of Ice leads the six guardians to Ireland, Doyle, the immortal, must face his tragic past. Three centuries ago, he closed off his heart, yet his warrior spirit is still drawn to the wild. And there's no one more familiar with the wild than Riley--and the wolf within her... An archaeologist, Riley is no stranger...

Oona the mermaid is friends with everyone, but when her attempts to befriend a shark with sensory issues fail miserably she realizes what may be fun for her may be overwhelming for him.

Oona and her best friend Otto love to search for treasure...and often find trouble instead. Messy trouble. Tricky trouble. Even shark-related trouble. That's never stopped them before, though! After all, no proper treasure hunt is without some adventure. But when the grandest treasure yet is stuck in a deep, dark rift, Oona's not sure if she can dive right in. What might be waiting for her in those unknown waters?