Dr. Kozak (Robert Downey Jr.) kidnaps a 300-year old Tibetan sheepdog in an attempt to discover the dog's secret of longevity and produce a fountain of youth drug. Unfortunately, all he has produced are animal mutations such as a king cobra-canine with a tail, a dog-frog that barks, and other mutations that are part dog. The sheepdog escapes the lab and is rescued by Carly Douglas (Zena Grey), who takes him home. Deputy District Attorney Dave Douglas (Tim Allen) is prosecuting Carly's teacher for the firebombing of Dr. Kozak's lab. Dave hates dogs, and after he is bitten by the sheepdog, the dog is sent to the pound. The dog has injected Dave with some of his DNA cells, and Dave begins to have canine urges and eventually, becomes a sheepdog. Dave learns the truth about his family and the drug company as a dog.