When their rival, Humdinger, becomes Mayor of nearby Adventure City and starts wreaking havoc, Ryder and the heroic pups kick into high gear to face the most challenging mission of their careers. Along the way, the team finds help from a new ally, the savvy dachshund Liberty, and together they fight to save the citizens of Adventure City! Can the pups save the city before it's too late? After all, no city is too big, no pup is too small!