Sunny and Rex are royal puppies! Sunny is a ladylike goldendoodle, and Rex is a mischievous beagle. They love living in the palace together with their owners and best friends, Princess Annie and Prince James. Now there's a new addition to the royal family—James and Annie have a baby sister! Unfortunately, little Baby Rose makes a whole lot of noise. On a rainy day at Glimmer Rock palace, everyone is stuck indoors, and no one can escape her cries. Sunny, Rex, and their new puppy friend Blix take refuge in the library, where they stumble on an old map of secret passages within the castle walls. Their drizzly day has turned into an adventure! As the puppies follow the clues on the map, they meet new friends, discover secrets hidden for centuries, and search for lost treasure!