Buck, by pulling the sled containing a thousand pounds of flour, made enough money to stake John Thornton, Pete, and Hans in their quest to find a storied lost mine. It is said an old worn shack marks the mine. John and his partners determine to find the mine, so they head out into the wilderness, looking for a mine no man has ever found.

John decides the journey will be at the pace set by him and his friends. They eat whatever they can kill or find along the way, which means some days they go hungry, while others they eat heartily.

Buck loves the trip, because it takes him off the known trails and into the wilderness. He revels in the hunting and fishing, also he is energized during the times they camp for weeks, allowing him and the other dogs to roam freely. They travel in this manner for over a year stumbling on false trails and finding the remains of old hunting lodges, but none of them are the opening to the mine they seek.

The second spring of their quest, they come across a shallow stream in a valley, which is loaded with gold. This is not the mine they are seeking, but it fills the desire to find enough gold to sustain them for a long time and they decide to make a permanent camp there. The three men work the find every day, loading moose-hide bags with gold nuggets and gold dust. The dogs are free to roam, unless they are needed to haul meat on the sled.

Buck during this time begins to feel a need to go into the forest, even though he doesn't know why he feels this pull to the unknown wilderness. The pull of the call of the forest will come upon him in his sleep, causing him to leave the safety of the camp for the dangers of the woods. He cannot control himself, instead he will run for hours through the woods and sit for a day watching partridges.

One night as he rushes into the forest, he hears a wolf howling; Buck approaches the wolf who tries to run from him. Buck is too fast and too big for the wolf to shake him and after chasing him for a time, the wolf decides to allow Buck to come near him. The two animals touch noses and sealed their friendship.

Buck and his wood brother run together, the wolf wants Buck to follow him to his pack, but Buck is held back by his devotion to John Thornton. He returns to John, even though being with the wolf gives him great joy and allows him to follow the call he feels compelled to answer.

After spending some days with John, Buck once again returned to the forest in hopes of finding his wood brother. Even though he searches the forest he cannot find him.

Buck becomes restless being in the camp and begins to leave to wander the forest for days at a time. He will kill for food, including killing a bear, Buck becomes a killer of great skill. He is faster than the other animals and can bring down any prey he desires.

He returns to John Thornton, every time he has had enough of the wilderness, but he is a changed animal. His senses are heightened, to the extent that he reacts to every situation with a quickness and ferocity unequaled by any man or animal. He loves being with John, but he also loves being in the forest.

When he leaves camp, he becomes a different dog, an animal who is wild and revels in his ability to kill, but he will only kill for food. He does tire of killing small animals and desires to find a more challenging opponent. This opportunity comes as the moose move down to the lower valleys in the winter. He finds an older bull moose, who is over six feet tall and the leader of his herd. This was the quarry he desires to kill.

He begins by trying to cut him from the rest of the herd, but the younger bulls come to their leader's aid, thwarting Buck's plan. After a day of dogging the old bull moose, the rest of the herd leaves him behind to fend for himself, after all they need to reach the lower valley before the harshness of winter sets in and leaves the herd vulnerable. Buck then chases and bullies the moose for four days, not allowing him to eat or drink, before he finally makes his kill.

On the way back to camp, Buck senses something is very wrong. The air is silent and he feels a foreboding as he makes his way back to John. He finds the men and dogs all dead, killed by men called the Yeehats. Upon sensing the demise of John Thornton, Buck goes into a killing frenzy, ripping out the throats of any Yeehat he can reach. He follows them as they try to flee into the woods. He becomes a legend among the Yeehats, they called him the Ghost Dog.

Buck, after killing the Yeehats, hears the howling of a pack of wolves. He defends himself against their attacks, until his wood brother approaches him and he is accepted into the pack. Buck mates with the wolves and spends the rest of his life with them. He does return every summer to the place John Thornton was killed and lets out one soulful howl for his fallen friend.

Buck lived his life with John Thornton giving him his utmost devotion. The only time he left John was to heed the beast in himself, who needed to run in the forest and be wild. The death of John and the others changed the course of Buck's life forever.