After Buck had made his master $1600 by pulling the sled laden with 1000 pounds, Thornton was able to begin a journey of which he had always dreamed: He and his partners would seek the fabled Lost Cabin mine. They spent the next two winters searching the Yukon for the lost mine, but it was never found. Instead, the men stumbled upon a "shallower place" that yielded more gold than they could have ever imagined. Every day the men worked created a yield of "thousands of dollars in clean dust and nuggets," and so the men decided to stay until they could mine all the gold they could find. The remoteness of the area led Buck to trail a pack of wild wolves, and Buck's call of the wild became greater than ever. And when Buck returned to camp one day to find everyone dead, he realized that it was time for him to leave the world of the humans and pursue the call.
After Buck wins $1600 for his master in a bet, the money enables his master to pay his debts and to pursue a long awaited trip to a fabled lost mine. Thornton and his partners expect to strike plenty of gold. However, not much is known about the mine, and both its existence and location are shrouded in mystery. The group sets out in search of the mine and to excel where others before them failed. Although their search does not bring them to the lost mine, it brings them to a valley that has plenty of gold on its surface. The group camps and sets to work, mining the gold. The dogs don't have much to do, and in this state Buck's call of the wild starts to grow stronger. Buck frequently leaves the campsite for days, but upon return from one of these trips, Buck finds the camp destroyed and all its members dead, including his master. The situation breaks off the final link between Buck and human beings, and the dog finally yields to the call and joins a pack of wolves.