Buck is at first at Judge Miller's house with his family, being there as if he is a "guard dog" for them. He is pondering about life, and is continuing to more acknowledge the Judge's gardener just a little bit more. He also now thinks more about his ancestors, calling out into the wild, about his own instincts.
Buck is now submerged back into the wild, and is reliving what his ancestors had once done before in their lifetime. He meets Francois and Perrault, who are not the nicest people. He goes through rough and hard-working journeys that teach him what it truly means to work for a living. He goes through many journeys as to who he is sold to and where he goes.
The land, once covered in thick, blanketed snow, is now melting, and the grass is showing through, because of springtime. Then, Buck meets a man named John Thornton who is the nicest, most loving man he has ever met in his entire life. Thornton gives him a lot of love, affection, and care. Buck helps Thornton with daily duties, and actually knows what it's like to truly be loved.
Buck and John Thornton's relationship progresses, and they go through more heartwarming and heart-wrenching times, with people he hates and admires. All of these events lead up to the point to where John Thornton is killed. Before Thornton was killed, Buck was continuing the ongoing war inside of his head that was him vs. the call of the wild.
Before, Buck had always chose that he would stay with Thornton, because he cared deeply for him. But, Buck saw Thornton's passing as an opening for him to be granted his way to answering the very strong call of the wild that he was trying very hard to not answer. He knew that it was time for him to finally go where he thrived and belonged to be. Buck takes off into the wild, being free, accepting his new fate, and loving it. He goes on a animal-killing rampage, which he runs at rapidly.