Arriving at Skagway from Dawson for the second time, only thirty days after they had departed, the dogs are in a wretched state. Along with the others, Buck has lost a lot of weight. They are all footsore, barely able to move. Months of constant toil have depleted strength and dissolved their muscle fibers. The men were tired as well and confidently told the dogs they would be getting a long rest. But, so many men had arrived at the Klondike that the men immediately received new orders, and were told to sell of their dogs and replace them with fresh ones.
Two men from the States, Charles and Hal, buy the dogs and the sled very cheaply. Neither man looks like he belongs. The camp is shabby and sloppy. There waits Mercedes, wife of Charles, sister of Hal. Buck watches apprehensively as they clumsily take down the camp, improperly rolling the tent, and loading up the sleigh unevenly. Two other men from a neighboring camp warn them that the sled is too heavy, but they will not listen. The team cannot move the sled. They are repeatedly whipped by Hal, as Mercedes cries over them. Buck does not like her, but tolerates her pleading pats.
When the sled finally moves,it falls on it's side. Raging at the unfair treatment, Buck leads the team in a run, scattering the belongings even further and running the sled over Hal. Finally taking the advice of those around them, they remove many of the superfluous luxuries, though Mercedes cries over them, and more dogs are added to the team. The journey begins. The new dogs are relatively useless -- Buck can teach them "what not to do," but he can't teach them "what to do."
Buck knows the team cannot depend on these people for they do their work inefficiently and crudely. They are barely traveling ten miles a day, and it is inevitable they will run short on dog food. When this occurs, underfeeding commences. One by one dogs are dying, first Dub whose injured shoulder grows worse and worse, than almost all of the new dogs. The men curse, and Mercedes cries. They lack patience and constantly argue with one another. Charles and Hal constantly fight over who does more work, Mercedes flightily changing her allegiance from husband to brother and back again. All too often the three began to quarrel before the camp was pitched, and it would remain unpitched until the quarrel had ended.
Mercedes has the additional crime of insisting that she ride on the sled. Her weight weakens the team further, until one day they cannot move at all. Despite this struggle, Mercedes refuses to walk, even when the men lift her off the sled and drop her in the snow. Eventually the dog food gives out completely, and Hall feeds the dogs strips of frozen horsehide. Now Buck moves through the snow as if in a nightmare. His glossy coat is matted with blood from the wounds Hal has inflicted with his club. His muscles are disintegrating. The others, there are seven left, are equally badly off.
One day Billie falls and cannot get up. Hal kills him with an ax and cuts him out of the traces. The team knows this fate approaches. The next day Koona goes, but the five remaining struggle on, despite their serious pains. The spring weather is beautiful, but no one can take notice of it. They all stagger into John Thornton's camp for a rest. John warns the travelers that the ice is thin, and the trail is likely to drop out at any moment. Hal refuses to listen, and calls the team to order. Only the merciless lashing of his whip can make any of them rise. But Buck remains on the ground. He refuses to move. Hal takes up the club, but Buck will not move. He is too numb.
Suddenly John Thornton springs upon Hal and drives him back, telling him that he will kill him if he hits the dog one more time. Hal tries to retaliate and gets his knuckles slashed for his troubles. John cuts Buck's traces, and the team proceeds. A quarter of a mile away, the ice breaks and the sled goes down, taking humans and dogs with it.
This chapter contrasts the readers conceptions of "civilization" and "wildness." When the dogs are sold to Hal and his relatives, their decline is rapid and painful. These people are described as "manifestly out of place." The author writes about them disparagingly (Charles has "weak and watery eyes," Hal is "callow," and Mercedes "flutters") because they have no business intruding upon the domain of the pioneer. Charles, Hal and Mercedes have become so "civilized" that they are unable to adapt to new conditions. They are not fit to survive in this world, and it is tragic that their unsuitability must take the dogs down with them. Now it seems London questions whether this life of toil and hardship is not happier for dogs and men. These people seem weak and pointless. They are unable to work hard or well. They do not understand that they rely on the dogs or that the dogs rely on them. They betray them on both counts by leaning on them too hard and by not ensuring that they have enough to eat. They also have little respect for other humans, for they are unwilling to take advice. They have no instincts, and so they are doomed.
Mercedes is a problematic figure. The "privilege of her sex" is sarcastically noted several times. She insists on all things unreasonable: having a tent, riding the sled. She does not listen to reason, evidenced by the fact that when she is removed from the sled, she sits in the snow and cries like a child until she gets her way. Her sympathy for the dogs demonstrates her total lack of understanding. She doesn't want Hal to whip the dogs, but she doesn't care that they must suffer in order to pull her luxuries. London's criticism may seem chauvinistic; however, one can see Mercedes beliefs about the feminine as constructions of civilization. If Mercedes had been willing to recognize that this was no place for gentlemanly behavior, she would certainly have been as capable as her brother and husband.
The importance of good leaders to the happiness of the pack is proven by the pack's quick disintegration under Hal. Whereas they formerly worked together, they are now at odds, sharing too little food and quarreling among themselves. London underscores the pitiful state of the dogs by contrasting their pain with his raptures about the beauty of spring. Nature is cruel. Despite its beauty, it remains as difficult and violent as ever. The pleasant heat of the sun creates the very conditions that will lead to the sled team's death.
When Buck alone survives Hal's folly, he is once again singled out as unique; he represents "survival of the fittest," for Buck is the "fittest" dog in the Klondike. Once tame and mild, he now trusts his instincts; he no longer fears even the club, for Buck has learned how to beat it. At first Buck's failure to rise at John Thornton's camp seems like a sign of death. It appears that his will to live has been crushed. But it almost immediately becomes clear that Buck chooses to lie still. He is refusing to go on, refusing to endure any more pain and risk for these untrustworthy, disloyal and weak people.
One might speculate as to why the other dogs continue to go. On the one hand, they are followers rather than leaders. On the other hand, Buck has knowledge that the others do not. He has lived among so-called civilized people. His instinct has made him wise in the ways of dogs, but his experience has made him wise in the ways of people. The other dogs know no life but the traces, or they have too much fear of the club. John sees Buck and understands his silent revolt. He saves him, because he recognizes his value. John knows the kind of loyalty and power necessary to survival in this kind of world. When the sled team goes down, the reader may or may not experience pleasure at the death of Hal, Mercedes and Charles, but the death of the dogs is poignant, even heart-breaking. Even more so than the single deaths thus far, this scene drives home the consequences of attempting to live in this world of club and fang.