Buck has been away from the camp for quite a while in chapter 7. He has been hunting all manner of creature, and the reader is told that his hunt and killing of the moose was a four day endeavor.
As Buck is returning to the camp he senses that something is wrong. His feelings are confirmed when Buck finds Nig and another dog dying along the trail. Buck keeps moving toward the camp and discovers that Yeehat Indians have destroyed the place and killed Hans. The Yeehat Indians are still there celebrating their victory. Buck attacks the group and kills a few of them before they scatter.
Buck's victory is a mixture of emotions for the dog. While he is proud of his victory over the Yeehats, his master, Thornton, is dead. However, his death allows Buck to heed the call of the wolf and join the pack.