In chapter seven, John Thorton and his two friends, Pete and Hans, embark on an expedition to a legendary gold mine in the North and take Buck and their other dogs along for the trip. After Thorton and his men strike gold, Buck begins to spend more time in the wilderness, where he ends up killing a bear and a moose. At this point in the story, Buck is beginning to behave more like a wolf than a domesticated dog and feels the urge to abandon his old life behind in order to run with the wolves and embrace the wild. One fateful day, Buck returns to Thorton's camp and discovers that his master has been brutally murdered by a group of Yeehat Indians. After discovering Thorton's lifeless body, Buck becomes incensed with fury and rage and proceeds to attack the defenseless Yeehats, who proclaim that Buck is an evil spirit. Overall, John Thorton is brutally murdered by a group of Yeehat Indians at his camp, which is deep in Northland away from civilization.

Buck has left John and the mining camp to go hunt and has decided that he will bring down a great old bull moose. As he follows it and harries it for days, the Yeehat Indians have attacked the mining camp and killed John. Buck knows nothing of this until he kills and feasts on the moose and then begins his journey back to camp. On his way there he begins to sense that something has changed. He notes that the animals are different and making different noises and singing different songs.

When he finally reaches the camp, the Yeehats are still there and he attacks them with an incredible ferocity. They were so terrified and he was so ferocious that they thought it was the evil spirit come to torment them.