Orphaned Tommy Ryan is informed that the money from his father's estate has run out, and he will have to leave the Holbrook Military Academy. Bunting, the dour superintendent,forces Tommy to leave his dog, Skippy, behind. But Skippt breaks away and catches up with Tommy. Tommy reads a newspaper story of a dog-show to be held in High Hills with a prize of $15,000. Reporter Bob Clayton, who is to cover the show for the New York Chronicle, picks up Tommy and Skippy and brings them to High Hills. In High Hills, Skippy darts across the street after a Chihuahua dog. Tommy runs after him and is knocked down by a station wagon driven by Dave Farmer and Skippy leaps at Farmer. Doc Ramsey, a vet, quiets Skippy and takes Tommy to his offices, while Bob and Lorna, Ramsey's daughter,follow. Policeman Manning appears investigating Farmer's complaint that Skippy is a killer-dog, but Ramsey assumes responsibility for the dog's good behavior. At the show, Tommy overhears Farmer being fired because Sands has just sold his dogs to Parker, who refuses to hire Farmer. Tommy finds that he can't enter Skippy in the show because he is not registered. Tommy and Ramsey break into the Kennel Club that night to sneak Skippy into a stall so that he will be judged in the show. A burglar alarm rings, the dogs all flee their stalls and Tommy and Ramsey are captured by the night watchman. All of the dogs are recovered except four valuable ones, and Tommy and Skippy escape from the police. Bob gets a phone call from Farmer to meet him at the Snodgras Lumber Yard where, for $100, he will tell Bob who has the four missing dogs. But Farmer is frightened away before he can talk. Bob, Lorna and Ramsey head for home but Tommy and Skippy see Farmer in the cemetery and trail him.Tommy slips in the mud and Skippy springs after Farmer and disappears. Later, Farmer is discovered dead, with a rip in his throat. Police Chief Taggart finds that Skippy has returned to Bob's house, injured. Bob prevents the police from killing the dog, demanding that he be tried. But, alas, there is too much circumstantial evidence against Skippy and he is sentenced to a humane death. and Tommy returned to Bunting's custody. That leaves Tommy, the Tenth Avenue Kid and his dog against the world, and the world is winning going away.