In the Warner Books publication, the pages are 88–90 for this incident. The passage is in Chapter 9 of To Kill a Mockingbird.
Scout's cousin Francis is not a relative of whom she is very fond. Scout finds it difficult to agree with Francis on several topics, one of which is Dill. Francis ridicules Dill, referring to him as "a little runt" who is merely passed back and forth from one relative to another in the summer. When Scout disagrees, Francis assumes a superior attitude and tells Scout,
"You're mighty dumb sometimes, Jean-Louise. Guess you don't know any better, though."
Scout detects the arrogance in the words and asks him what he means. He responds,
"If Uncle Atticus lets you run around with stray dogs, that's his own business, like Grandma says, so it ain't your fault. I guess it ain't your fault if Uncle Atticus is a n****r-lover besides, but I'm here to tell you it certainly does mortify the rest of the family--"
An instantly incensed Scout challenges him to clarify his statement. Francis says, "He's ruinin' the family, that what he's doin'." He rises and gets a safe distance before he shouts that Atticus "is nothin' but a n****r-lover!"
Now it is an extremely belligerent Scout who leaps from the steps and races down the catwalk where Francis has gone. She grabs him and demands that he take back his insult. Francis refuses and jerks himself loose. Racing into the old kitchen, he yells back at Scout, repeating his invective.
This time she connects with her fist and splits the skin of her knuckles on his front teeth. Then she swings with her right fist, but Uncle Jack grabs her arms before she can connect with her punch. When he scolds her, Scout complains that he is not being fair because he does not know what Francis has called Atticus.
Later, Uncle Jack comes to the Finch home and talks with Scout; after hearing her side, he promises to have a talk with his sister Alexandra about the behavior of Francis, and he adds, "Wait'll I get my hands on that boy...." But Scout begs her uncle to not say anything about Francis's name-calling. He promises, restoring his and Scout's amicable relationship again.