After a young red fox is orphaned, Big Mama the owl and her friends Dinky the finch and Boomer the woodpecker, arrange for him to be adopted by kindly farmer Widow Tweed, who names him Tod. Meanwhile, Tweed’s neighbor, hunter Amos Slade, brings home a young hound puppy named Copper and introduces him to his hunting dog Chief. One day, Tod and Copper meet and become best friends, pledging eternal friendship. Slade grows frustrated at Copper for constantly wandering off to play, and places him on a leash. While playing with Copper outside his doghouse, Tod awakens Chief. Slade and Chief chase Tod until they are stopped by Tweed. After an argument, Slade threatens to kill Tod if he trespasses on his farm again. Hunting season comes and Slade takes his dogs into the wilderness for the interim. Meanwhile, Big Mama, Dinky, and Boomer attempt to explain to Tod that he and Copper will become bitter enemies. In denial, Tod naively refuses to believe them, hoping that he and Copper will remain friends forever.
The following spring, Tod and Copper reach adulthood. Copper returns as an expert hunting dog, who is expected to track down foxes. During the night, Tod sneaks over to talk to Copper. Copper warns Tod that Chief will hunt him down if awakened by their conversation, and Chief indeed is awakened. Chief alerts Slade and a chase ensues in which Copper catches Tod. Copper lets Tod go while diverting Slade, while Tod attempts an escape on a railroad track. Chief, however catches Tod and gives chase, but an oncoming train strikes Chief. Chief falls into the river below, breaking his leg. Enraged by this, Copper and Slade blame Tod for the accident and vow vengeance. Realizing Tod is no longer safe with her, Tweed leaves him at a game preserve.
Tod’s first night alone in the woods proves disastrous, as he inadvertently trespasses into an irritable old badger’s den. Thankfully, a friendly porcupine offers Tod shelter. That same night, Slade and Copper plan to poach Tod. The next morning, Big Mama finds Tod and introduces him to a female fox named Vixey, who helps Tod adapt to life in the forest.
Meanwhile, Slade and Copper trespass into the preserve to hunt Tod. As Tod manages to escape Slade’s leghold traps, Copper and Slade pursue both foxes. They hide in their burrow while Slade tries trapping them by setting fire to its entrance. The foxes narrowly escape the burning burrow as Slade and Copper chase them up the top of a hill until they reach a waterfall. There, Slade and Copper close in for the kill, but a large bear emerges and attacks Slade. Slade trips and falls into one of his own traps, dropping his gun slightly out of reach. Copper attempts to fight the bear but is no match for it. Not willing to let his former friend die, Tod intervenes and fights the bear until they both fall down the waterfall.
With the bear gone, a bewildered Copper approaches Tod as he lies exhausted near the bank of a waterfall-created lake. When Slade appears, Copper positions himself in front of Tod to prevent Slade from shooting him, refusing to move away. Slade lowers his gun and leaves with Copper. Tod and Copper share one last smile before parting. At home, Tweed nurses Slade back to health while Chief and Copper rest. Copper, before going to sleep, smiles as he remembers the day when he first met Tod. On a hill, Vixey joins Tod as they look down on the homes of Slade and Tweed.