Herk is happy to have a new family and a new place to call home. But when the Lizzarks make an all-out assault on Amphibopolis using a giant monster, Herk must seek the help of the megasloth to save the city and his adopted family. Meanwhile, Sissy, Herk's sister, discovers the dark truth about their long-lost brother Zerk--and truth that will affect Herk and the future of all Nnewts.