They’ve done it again! In this ninth installment, the Hales have brought back all the elements young readers love about the “Princess in Black” series—heroes in disguise, hungry monsters, imperiled goats, and ninja skills—but this time, they’ve set their story underwater, added a mermaid princess, and included a powerful message of speaking up to help others. . . young readers will eagerly dive into this latest series adventure.
—School Library Journal (starred review)