Celeste the Cat is tormented by her human's insistence on keeping a dwarf hamster, appallingly named Celestina, as a pet. Enlisting the aid of two friends, the brave but intellectually challenged Tiger and overly-enthusiastic Ruby, she sets out to trap a giant hamster that is loose and living in a nearby field. She plans on placing the giant hamster in front of Celestina's cage to show her owner what she thinks of pet rodents. The giant hamster--actually a capybara--proves to be a larger, stronger and more intelligent adversary than the cats expect, resulting in a series of humorous mishaps that leave the trio battered but not dispirited. Slowly the cats come to realize that the capybara is not the frightening monster they imagined. When the capybara has a litter of eight precocious capy-kittens, Celeste, Ruby and Tiger find themselves doing things they never imagined, like going for a swim and protecting baby rodents from a tough gang of tom cats.