When the Wright family moves into their new home, Russel is surprised to find a secret passage under his bed. This passage leads him and his dog Gus to the world of Under, where he discovers he is the new King and that Gus can talk! Russel and Gus quickly befriend the people and creatures of this mysterious land. Bob Wire and his evil team are continually conspiring to steal Russel's crown and become all-powerful rulers of the land.