During the late 19th century Gold Rush, Buck, a large and gentle St. Bernard/Scotch Collie, enjoys a peaceful life with his master, Judge Miller, in Santa Clara, California. However, one fateful night, Buck is forcibly taken from his home, destined for a life of servitude in the Yukon aboard a freighter. The journey is brutal, as a crew member harshly mistreats him by beating and starving him. Once in the Yukon, Buck's fortunes begin to change when he returns a fallen harmonica to a man named John Thornton, moments before being sold to Perrault and his assistant, Francoise. They embark on a treacherous journey across the icy expanse of the Yukon, delivering mail via dog sled, with Perrault eager to meet tight deadlines.
As Buck integrates into his new life, he meets the other sled dogs, including the fierce pack leader, Spitz, a Husky bent on asserting dominance. Throughout their arduous travels, Buck forms a bond with Francoise after saving her from a perilous situation on the ice, and gains the trust of the other sled dogs. However, trouble brews as Spitz grows increasingly hostile. In a pivotal moment, Buck confronts and defeats Spitz, claiming the role of pack leader when no other dog steps up. With Buck at the head of the team, their sled arrives at the mail depot just in time to deliver their cargo. Here, Thornton shares a heartfelt letter to his late wife regarding their deceased son, further deepening the emotional connection between him and Buck.
Soon after, Perrault learns that the mail route will be replaced by the telegraph, compelling him to sell the dogs. The corrupt Hal, played by [Dan Stevens], purchases Buck and the team, forcing them to endure grueling conditions while hauling heavy loads. Exhausted, the dogs halt at the edge of a precarious frozen lake, but Hal insists they continue. When Buck refuses to budge, Hal resorts to threats, prompting Thornton to intervene and rescue Buck while the other dogs are sent across the treacherous ice.
Resting under Thornton's care, Buck begins to recover. A confrontation at a bar leads to Hal attacking Thornton, who is betrayed by the very dogs he relied on. Witnessing the assault drives Buck into action; he retaliates against Hal, who later becomes obsessed with hunting down Thornton, believing he’s hoarding gold. As the chase unfolds, Buck and Thornton venture beyond the Yukon map, discovering an abandoned cabin in a vast, open valley where they decide to stay.
In the serenity of the wilderness, a bond forms between Thornton and Buck as they engage in daily pursuits like fishing and gold panning. Yet, Buck feels the pull of the wild, especially drawn to a female white wolf. Torn between his life with Thornton and the wolf pack, Buck finds himself at a crossroads. Thornton, sensing the impending return to civilization, tells Buck it’s time to leave, inviting him to say farewell. That night, Buck seeks the solace of the forest, lying next to the white wolf, caught in a state of conflict.
Tragedy strikes when Hal finds Thornton and shoots him fatally. Enraged and grieving, Buck retaliates, confronting Hal and pushing him into the cabin, which is engulfed in flames. In his dying moments, Thornton urges Buck to live for himself, expressing, > "It's okay, boy. You're home."
The following day marks a new beginning for Buck, as he finally heeds the call of the wild. He embraces life in the wilderness, mating with the white wolf and taking on the mantle of pack leader, thus fully realizing his true nature.
