The money that Thornton won from the bet provided him the opportunity to pay off his debts and leave with his friends to look for a gold mine that was shrouded with mysterious stories. Many men were unsuccessful in their attempts at finding it and Thornton was eager to try his luck.
After several years of traveling and simply having a wonderful time at fishing and hunting, the men finally came to a valley "where the gold showed like yellow butter across the bottom of the washing-pan". They decided that this was a good enough place for them to pan for gold and began to work there on a daily basis.
With the men being busy, Buck was left to his own devices and started to explore the wilderness on his own. Sometimes he stayed away for several days and learned to survive on his own by catching salmon. One day he even killed a black bear as well as two wolverines who tried to feed on "his" bear. After each incident, his "blood longing becomes stronger" and his desire to kill increased. Slowly he seemed to shed more and more of his civilized mannerisms.
On one of his sojourns into the forest, he met a wolverine and they became friends. He stayed away from camp longer than usual and enjoyed every moment of it. One day he felt that something was different. Following his instincts, he decided to return to Thornton. When he neared the camp, he sensed that something was amiss. He found Nig lying dead on the ground and he heard strange sounds as he came closer to the campsite.
Gathered around the fire, he saw a group of Yeehats celebrating their conquest. He also saw Pete lying face down with arrows sticking out of him. Realizing what had happened, Buck fearlessly hurled himself at the men. He did not heed the arrows that were flying around him and killed most of the Indians. The ones that were able to escape his ferocious attacks scattered in the forest.
Buck chased them a while longer but then returned to the deserted camp. After searching around, what he suspected became a reality and he saw the trail that Thornton left as he was struggling to the bitter end. The scent of his master led Buck to the edge of a pool into which Thornton's body had fallen. Buck was stricken with a great sense of loss and sadness but also with a sense of pride that he had been able to revenge his master's murder.
His grief was overwhelming and he stayed in the area quite a while until he heard strange noises coming from the forest. He knew that he had accomplished a great fete as he was able to kill armed men, the greatest "game" of all and he remained calm and unafraid. Soon he saw what was causing the noise as a wolf pack came into Buck's area. He stood his ground unafraid and in only a few moments, he was accepted by the pack. He was also greeted by his companion whom he had met previously when he went on his trips into the forest. Buck left the campsite and joined the pack of wolves. With this act, he turned his back on civilization and followed "The Call of the Wild".
To this day, there is a legend that is spread by the Yeehats that an "Evil Spirit" lurks in the valley and can be seen at a certain spot by the edge of the water.
The final chapter of the novel shows how Buck is drawn more and more into the wilderness. Even though he does not want to leave Thornton completely, he does stay away from camp for several days on many occasions and stays in the woods. His inner instincts dictate to him and he hunts and kills.
On an occasion when Buck was away from camp Thornton is murdered by a group of Indians. When Buck returns to the camp and realizes what has happened, he ferociously attacks the men and kills most of them.
Although Buck is heartbroken over having lost his friend, he feels that he is now able to follow his instinct and answer the call of the wild.