The Shaggy Dog
Dave Douglas (Tim Allen) is a deputy district attorney, whom viewers see prosecuting activists who have broken into and allegedly set fire to the laboratory of pharmaceutical corporation Grant and Strictland, which the activists accuse of deliberately creating genetic freaks while searching for a "Fountain of Youth". This distances Douglas from his activist daughter Carly (Zena Grey).
Viewers learn that the power-hungry minions of Mister Strictland (the surviving but aged junior partner of the late Grant), led by Dr. Kozak (Robert Downey Jr.), have stolen from a Tibetan Buddhist monastery the dog Khyi-yag-po (played by a bearded collie), whose DNA carries a mutation granting an extraordinary lifespan. Seeking to obtain his seeming immortality for themselves, the geneticists carry out several experiments which fail comically; though cell degradation desists in all the test subjects (a bullfrog with a head of a bull, rats who behave like cats, rabbits who behave like kangaroos, a chimpanzee who behaves like a human being, a cobra with a chameleon-like tail, and a capuchin monkey who behaves like a spider). The scientists determine that Khyi-yag-po's mutation is contagious and transmissible by bodily fluids.
Khyi-yag-po later escapes his cage and is found by Carly Douglas and her friend Trey (Shawn Pyfrom), who are trying to find evidence of the company's animal testing. They bring him home and dub him "Shaggy". When Dave returns from work, he objects to the dog's presence and orders it out, but in the process is bitten on the hand, whereupon Khyi-yag-po's saliva enters Dave's veins, infecting him with the mutation.
Dave thereafter begins to exhibit canine behavior such as eating with only his mouth, being territorial in the presence of other dogs, and licking his wife rather than kissing her. When he becomes excited by stimuli associated with dogs, such as the command "Fetch!" or the presence of a cat, he transforms completely into a replica of Khyi-yag-po. This change is reversed only when he has calmed, as during sleep. When the real Khyi-yag-po is caught by Kozak's lab minions, Dave is mistaken for "Shaggy" and takes his place. His family, ignorant of this, speak freely in his presence, leading Dave to realize that he is estranged from them. In particular, he learns that his son Josh (Spencer Breslin) wants to sing in the musical Grease instead of playing football, but is too scared to tell his father so.
In the ongoing trial, testimony from the activist accused of setting the lab on fire includes a description of the animals behaving like dogs, which sparks Dave's suspicions about the company he is defending. When his dog-like behavior annoys the judge, Dave is removed from the case. He then decides to take matters into his own hands and infiltrates Grant and Strictland headquarters while in his canine form.
Hidden in the laboratory, Dave witnesses Dr. Kozak injecting the ailing Strictland with a drug that will paralyze him for several months, giving Kozak enough time to usurp control of the company. After viewing security cameras, Kozak and his minions realize that somehow Dave Douglas was able to become the exact copy of Khyi-yag-po.
When Dave comes home, still in his canine form, he overhears a conversation between Carly and Josh that Dave and Rebecca are splitting up. After hearing this Dave then knocks over a Scrabble and then used the letters to spell "I AM DAD" to his children, then spells "GRANT AND STRICTLAND" to them, making them realize the truth. Unfortunately when Dave gets out of the house, he is captured by Kozak's minions.
After the humans leave, Dave and all the other mutants plan to escape. Acting on Khi-yag-po's advice, Dave calms himself, then in human form breaks open his cage and opens the others. They all pile into a car and drive to the courthouse, but get into traffic making Dave leaving animals to drive while he meets his wife and children in his canine form. Dave says he loves them, then turns into his human form.
In the court room, Dave attempts to show the assembly what Kozak has done, but only succeeds in doing so when he tricks Kozak into growing a tail. Grant and Strictland Corporation is thrown into disgrace, and Dave is able to spend more time with his family, though some of his canine habits remain. Hidden in the credits is a scene showing Kozak escaping from jail, to presumably return in a sequel.
