Shoeshine (Jason Lee) is an ordinary young Beagle dog who accidentally obtains superpowers as the result of a lab accident of the evil Dr. Simon Barsinister (Peter Dinklage). He is then adopted by 12 year-old Jack (Alex Neuberger) and begins to protect Capitol City as 'Underdog' and tries to win the heart of a Spaniel named Polly Purebred (Amy Adams). But Dr. Barsinister has devised a sinister plot with his henchman Cad (Patrick Warburton) to destroy the city and only Underdog can save the day.