The story begins when a klutzy police beagle is accidentally kidnapped to be a guinea pig to Capitol City's best geneticist Simon Barsinister (Peter Dinklage), who is secretly experimenting on dogs to perfect his serum. However, the beagle escapes, but not before causing a lab fire and being exposed to various substances. Found by Dan Unger (Jim Belushi), the beagle is named "Shoeshine" and becomes the pet of Dan's son, 12-year-old Jack Unger (Alex Neuberger). But as both eventually learn, the incident at the lab has not only made Shoeshine able to speak, but also able to fly and possess superhuman strength. Jack convinces Shoeshine to use his superpowers to help the citizens of Capitol City, taking the name "Underdog." However, Barsinister, hunting after Underdog and eventually learning of his identity, manages to use the Ungers to force Underdog to provide a sample of his DNA that the scientist uses in the form of pills and an antidote that he uses on Shoeshine to turn him back to a normal dog. After feeding three of the pills to his German Shepherds, Barsinister takes the mayor hostage while Cad sets up a bomb on top of city hall. However, Shoeshine manages to regain his powers, turn the German Shepherds against Barsinister and save the day.