From publicity material: When the selkie twins, Ronan and Muriel, leave Petaybee on a mission to help rescue a family friend, they end up imprisoned themselves: the Company wants them for workers, while an unscrupulous scientist wants to study their unusual shape-changing ability. Meanwhile, the Company is making another attempt to take over the world of Petaybee for its resources, and the twins' parents, Yana and Sean, must fight for the independence of their sentient world once and for all ...

(Source: Del Rey)