Rex Allen, a government veterinarian, is filling in temporarily in the town of Pine Rock near the Canadian border. Shortly after Rex arrives, Slim Pickens, the town's dog-catcher and vet's helper, informs him that the job traditionally includes certifying wild foxes that are caught in Canada during a fox hunt, an event run by Steve Baxter, the owner of a Canadian trading post. After being hunted, the animals are transported in crates into the United States for breeding at Mel Richards' silver fox farm. Rex agrees to the task and while on the Canadian side of the border, meets Constable Gene Dalton, who is trying to solve a case involving counterfeit U.S. money made in Canada. Later at the fox farm, Mel's niece Jane gives Rex a tour, as Mel and other workers uncrate the foxes and stack the empty crates in the barn. The crates have false bottoms which are filled with counterfeit money, and Mel has planned a pelt auction for the next day through which the money will be laundered. Mel, who is the guardian of Jane and her school-aged brother Danny, tries to discontinue his association with the counterfeiter, Baxter, but Baxter threatens to implicate the children in the crimes. Meanwhile, Rex finds that Danny's pet fox, Smoky, is sick, and when the pet's condition worsens the next day, prepares to take it to the office for tests and quarantines the rest of Mel's animals and pelts. With the auction plans disrupted, Baxter's partner, Matt Lacey, fights Rex until Rex knocks him out. Realizing Rex cannot be bribed or fooled, Baxter and Lacey arrange for men to steal Smoky from the vet's office, believing that without evidence, Rex will have to lift the quarantine. As Baxter's henchmen steal the fox from the vet's office, they also take Slim's pants and boots to keep him from following. Rex arrives as the thugs are leaving and follows them, along with Slim, wearing only his long johns. After the thugs release Smoky in the woods, Rex shoots one of them and tries to question him, but the injured man is killed by his own cohorts to keep him from talking. Barefoot Slim takes the dead man's boots, then he and Rex deliver the body to Constable Dalton, who identifies the man as a trapper who often visited Baxter's trading post. Rex returns to Mel's farm determined to examine every animal, and while he is undertaking his inspection, Baxter arrives and invites everyone to a barbecue. Secretly Baxter tells Mel that his men will retrieve the counterfeit money while everyone is at the party. Later at the vet's office, Slim finds several large bills in the dead man's boots and shows them to Rex, who suspects they are counterfeit. At the barbecue, Rex shows the money to Dalton, who confirms Rex's suspicions. Rex wonders if the quarantine trouble, the stolen fox and the counterfeiting are connected. After Slim tells Danny about Smoky's abduction, Danny sneaks off to search for his pet. He finds the fox in the woods and returns him to the farm, where he encounters the thugs, who take him to Lacey's place. Baxter is told by his henchmen that Danny saw them, and he regretfully orders that the child be killed. Meanwhile, the others discover Danny is missing, and when Mel realizes Danny was at the farm, he angrily confronts Baxter, who kills him. At the farm, Rex examines Smoky, and notices the false bottoms in the empty, broken crates. He and Slim round up Dalton, and the three race to the trading post. Though a fight ensues, the thugs are apprehended and admit that Danny was taken to Lacey's place. Rex, Lacey and Slim get to Lacey's as Danny and the money are loaded on a wagon. One of the thugs is shot and the other surrenders, but Baxter races away with the wagon. Baxter tries to shoot Rex, but Danny pulls him off balance. As Danny stops the horses, Rex overtakes Baxter. After Mel's body is found by Dalton, Slim makes plans to help Jane and Danny run the fox farm. With the regular veterinarian soon to return, Rex rides off to his next assignment.