It may be differ from book to book, but it should be chapter 6, page 79.
The challege Sara faces is that she had to decide whether or not to help the lady she saw on the trail, even though she was too scared.
The passage is centered on the theme of belonging in a certain pack or group. Buck may be a bit different from the others but as Buck tried to be like them and did what they usually do, it gathered the trust of the pack especially the leaders. To belong in a group, one should gain their trust.
