When Courage becomes depressed, Muriel takes him a veterinarian who turns out to be a dognapper, and it's up to Courage to foil his nefarious plans. Then, Eustace takes Courage to a doggie disciplinarian who is impossible to please.
Courage finds an old book that turns Eustace and Muriel into characters from it. Also: when the family goes sightseeing in Hollywood, they literally fall into the belly of the beast through a manhole in the street.
Eustace, envious of the attention Muriel lavishes on Courage, decides to get rid of the dog and consults four of Courage's enemies to do so. Also: alien naturalists take Eustace, Muriel and Courage back to their planet as specimens from Earth.