West of the sea / Stephanie Willing.

"When her mom disappears from their small Texas town, paleontology-loving Haven is determined to find her. But as she uncovers truths about her mom's identity, Haven also uncovers a monstrous family secret. Her mom can take the shape of a human and, in the right environment, also turn into an amphibious creature known as a kitskara. And now that she's growing up, Haven is discovering she has this ability, too. This newfound identity is her only clue to help her track her mother and bring her back home. And so she, her older sister Margie, and her new friend Rye set off on a road trip across Texas's Gulf Coast to her late grandparents' abandoned home, where they're sure her mom has disappeared to ... along with plenty of family secrets"--

Ages 8-12