Young Marty Preston lives in a remote rural community. There's not much to do during summer vacation but shoot cans and hang out with Sam, who's not too bad even if she is a girl. But Marty finds a purpose to his life when he meets a beaten and frightened beagle he names Shiloh and decides to fight to keep him from being returned to his abusive owner.

After an accident in the lab of the maniacal Dr. Barsinister, an ordinary beagle named Shoeshine finds he has some unimaginable powers, along with the ability to speak. Underdog vows to protect the citizens of Capitol City, and one beautiful spaniel named Polly Purebred.