Buck's first owner is Judge Miller, who lives in the sunny Santa Clara Valley. Buck enjoys his carefree life on the "sun-kissed" estate, where he rules over the territory and goes on playful hunting trips with Judge Miller's grandchildren. Unfortunately, Buck is stolen by Judge Miller's gardener Manuel, who takes him to Seattle, where Buck is broken by a brutal man in a red sweater. Buck is then sold to two French-Canadians named Francois and Perrault. Francois and Perrault are experienced mail couriers, who drive their sled dogs through the unforgiving Northland. Under Francois and Perrault's care, Buck develops into a skillful sled dog and helps the sled team break records. Both Francois and Perrault are depicted as humane, respectful owners, who value their dogs but push them hard to make deliveries.
In Skaguay, Buck is sold to another mail courier called the Scotch half-breed. Buck suffers under the Scotsman's care and is exhausted from carrying extremely heavy loads. Unlike Francois and Perrault, the Scotsman is not humane and pushes the dogs to their limits. Buck is sold once again to an inexperienced group of owners named Hal, Charles, and Mercedes. They are depicted as ignorant, cruel owners, who exhaust their dogs and place them in compromising, dangerous situations. Fortunately, John Thornton saves Buck from meeting a disastrous fate with Hal, Charles, and Mercedes as they proceed to break through the thin ice.
John Thornton becomes Buck's last owner, and he thrives under his care. John Thornton is portrayed as a loving, sincere master, who truly cares about Buck's well-being. Buck and John Thornton have an amazing relationship founded on love, loyalty, and respect. Buck accompanies John Thornton on many adventures, and John is depicted as the ideal master. Tragically, John Thornton is murdered by a group of Yeehat Indians, and Buck eventually submits to the call of the wild following his death. By the end of the story, Buck runs free in the wilderness with the wolves.