The next day, François and Perrault discover that Spitz is missing, and the signs of battle on Buck's body are proof that the inevitable battle between Buck and Spitz has occurred, and that Buck is the obvious winner. François is pleased because he knows that now there will be no more trouble with the dogs working as a team. A major decision must be made, however. Since Spitz has been killed, the sled drivers require a new lead dog. Sol-leks is chosen as the new lead dog. But Buck will not allow this, and he springs upon Sol-leks in a fury, indicating his desire to be the leader of the pack. François separates the dogs several times, but his tries are futile because Buck attacks Sol-leks again and again. Finally, François gets a club and threatens Buck with it. Buck immediately remembers the man in the red sweater, and he cowers before the club. Yet "Buck was in open revolt," and he springs upon Sol-leks at the first opportunity.
Perrault and François chase Buck around the camp site for about an hour, but Buck easily eludes them. Then realizing that they are losing precious time, the drivers finally yield to Buck's wishes and install him as the lead dog. Buck more than proves his prowess. Immediately, he "shows himself" the superior even of Spitz, of whom François had never seen the equal.
Buck continues to excel in leadership, and the other dogs fall immediately in line and grant Buck his hard-earned superiority. In fact, one of the dogs, Pike, lagging during the day, is soundly punished by Buck for his laziness. Thus the team begins operating in its old superior form, a fact which pleases François and Perrault very much. At one of the stops, the Rink Rapids, two native huskies, Teek and Koona, are added to the team, and Buck immediately coerces them into being members of the team. In record time, the journey from the Rink Rapids to Skagway, their destination, is accomplished.
For three days, Perrault and François brag about their accomplishments, and "the team [is] the constant center of a worshipful crowd of dog busters and mushers." New orders, however, come to the kindly drivers, François and Perrault, and "like other men, they are forced to accept new assignments, and so they leave Buck's life. Buck's new owner is a "Scotch half-breed" and is known only by that name; he is the driver of the mail team over the trail to Dawson. Once again, Buck and his mates set out on the weary and monotonous trail to Dawson. We are told that Buck enjoyed lying near the campfire, at which time he would dream of his old life in the Santa Clara Valley, but — and this is an important point — "he was not homesick." The Sunland was very "dim and distant," and such old memories have no power over him any more. At other times, he ponders the "half-breed cook" who also sits near the campfire. In London's description of the "half-breed cook," it is clear that he wants us to see the half-breed as a type of prehistoric cave man covered with hair, a creature perhaps closer to the animals than to the humans. We are told that "he did not stand erect," but that he had "a trunk that inclined forward from the hips on legs bent at the knees." He is described as a "hairy man" who slept with his "head between his legs."
Buck and his mates are in poor condition due to the lack of rest and recuperation at Skagway, and to make matters worse is the fact that on the way to Dawson, it snows every day, making the journey even more tedious. Once again, London reminds us of his central concern about the survival of the fittest. He tells us that since Buck's career as a sled dog began, he has traveled over 1800 miles, and that 1800 miles will take its toll — even on "the life of the toughest."
One day, Dave, one of the sled dogs, becomes irritable and constantly cries out in intense pain. The drivers can locate no broken bones or visible wounds, but they know that something is wrong, probably internally. The Scotch half-breed, therefore, decides to remove Dave from the team; yet Dave, even in his pain, is resentful. London explains that "the pride of trace and trail was his, and, sick unto death, he could not bear that another dog should do his work." So he runs alongside the sled, which causes him excruciating pain because he deeply desires to be a member of the team. The driver is concerned by Dave's actions, and his comrades "talked of how a dog could break its heart through being denied the work that killed it." The driver decides to harness Dave again, even though he knows that it will surely kill him. The next morning, Dave is too weak to travel, but through an incredible act of physical stamina, Dave bravely stands in line to be harnessed. He constantly trips and falls, and he stumbles, unable to pull along with his teammates, and at last, the driver is forced to remove Dave from the team. Retracing his steps to the camp, the Scotch half-breed takes Dave back with him, and as Buck listens from a distance, there is a crack of a revolver, ending Dave's life on the trail.
In general, this chapter functions as something very much like a transitional chapter. In the first three chapters, we saw how Buck adjusted to the primitive wilderness and to the primeval North. After his winning his mastership in this chapter, we see that Buck now performs the tests of his masters with perfect precision, making himself a lead dog superior even to all the other dogs. Thus, Buck proves to be a perfect creature. This transitional chapter contrasts with the first three chapters, then, and the next three chapters will show Buck becoming increasingly alien to all traces of civilization and preparing himself to accept and adapt to "the call of the wild."