The young heroes of Changelings (2005) depart the planet Petaybee, then return for more adventure.
Twins Ronan and Murel are changelings, able to take seal form on their home planet of Petaybee, which is sentient and adapts to its inhabitants. The book begins with the twins leaving Petaybee on a spaceship as ambassadors to help the people of the planet Halau, who will be relocating to Petaybee. But when they arrive, Halau has been hit by meteors and its settlements destroyed. A rescue is mounted, led by the twins, who turn into seals to rescue people in the water. Halau's people are brought aboard the ship. Back at Petaybee, while trying to help Halau refugees adapt to the odd environs, Ronan is kidnapped by some very strange sea creatures who have masqueraded as deep-water otters, but are actually aliens. Murel and her family have to save Ronan, while trying to keep various intelligent animals in Petaybee's ocean from eating each other—and them—during the search.
The characters are somewhat over-earnest and preachy, but the conversations between natural predators and prey make this an enjoyable.