“Brownies” takes place at Camp Crescendo, a summer camp for fourth graders near the suburbs of Atlanta, Georgia. The story is told in the first person by an African American girl named Laurel, known to the other girls by her nickname, Snot. Laurel announces that by the second day at the camp, all the girls in her Brownie troop had decided they were going to “kick the asses” of every girl in Brownie Troop 909, who were all white girls. The black girls took a dislike to the white girls when they first saw them. Arnetta, the girls’ ringleader, said they smelled “like Chihuahuas. Wet Chihuahuas.” When she adds that they were like “Caucasian Chihuahuas,” all the black girls go into fits of laughter. They regard the word Caucasian as a hilarious term of abuse that can be used in almost any situation.

The black girls have seen whites before but have never had much to do with them. But the ten white girls they encounter at the camp are closer to them and, therefore, more real and capable of exciting envy and hatred.

At the end of the first day at camp, Arnetta reports she heard one of the white girls refer to Daphne, a black girl, as “a nigger.” On prompting by Arnetta, Daphne, a quiet girl, nods her head to confirm that the derogatory term was used. Arnetta tells the other girls that they cannot let the white girls get away with using that word about them. She says they must teach the white girls a lesson. Janice suggests that they put daddy-long-legs in the white girls’ sleeping bags, and when the girls awake, beat them up. Arnetta tells Janice, who is not a popular girl, to shut up. Arnetta then announces that they are to hold a secret meeting. She turns to Laurel, whom she appears not to like, and asks her whether Laurel plans to tell Mrs. Margolin, their troop leader, about the situation.

On the second day of camp, the black girls eat their sandwich lunch by a stream that borders the field hockey lawn. Arnetta eyes the white girls from Troop 909 and would like to attack them right then and there, but the white girls are with their troop leader, which makes the mission impossible. When the white girls leave, Arnetta says they must find a way of getting them when they are alone. Laurel says that the girls will never be alone, and the only time they will be unsupervised is in the bathroom. Octavia tells Laurel to shut up, but Arnetta seems to think this is a useful piece of information.

The black girls walk to the restrooms, which are messy, with leaves and wads of chewing gum on the floor. Arnetta says that when they meet the white girls there, they will be nice to them at first and then tell them what happens when they call any one of the black girls a “nigger.” Janice says that she will tell the white girls, “We’re gonna teach you a lesson!” Laurel, who is normally very quiet, asks what will happen if the white girls say they did not use the offending word. Arnetta dismisses this possibility and says that all they have to do is fight. An exception is made for Daphne, however, since they are doing this to avenge her. The girls leave the restrooms, although Daphne stays behind, picking up the trash. When Arnetta is asked about the secret meeting, she replies that they have just had it.

That evening, just before their bedtime, Mrs. Hedy, the parent helper, comes to their cabin. The girls, knowing she is depressed about her impending divorce, sing her favorite Brownie song for her. The girls are then reluctantly persuaded by Mrs. Margolin to sing “The Doughnut Song,” a religious song which they all hate. Mrs. Margolin is tired and leaves to go to the lodge. Arnetta says it is time to go to the restroom, hoping that Mrs. Hedy will not go with them. Arnetta knows that the troop of white girls will be in the restrooms soon and will not be expecting an ambush. Mrs. Hedy indicates that the girls can go to the bathroom unaccompanied. She makes Octavia promise to be good.

Daphne tells Laurel that she is not going with them, and Laurel says she is not going either. But Arnetta overhears her and insists that she comes.

They make their way to the restrooms in the darkness, using a flashlight to guide them. They do not talk about fighting; they are all frightened enough to be walking through the woods at night.

When they arrive, the white girls are already there. Arnetta and Octavia go in first, instructing the others to follow when they hear Arnetta say, “We’re gonna teach you a lesson.”

After about a minute, Laurel hears one of the white girls deny that they had used the offensive word. The other black girls decide to go inside, even though Arnetta has not given the signal. Inside, they see five white girls huddled up against a bigger girl. Octavia whispers to Elise that she thinks the white girls are "retarded." The big girl denies it, but it is obvious to the others that she and all the other white girls are indeed mentally handicapped. Arnetta says they are just pretending, but Octavia, deflated, says that they should just leave. Octavia tells the big girl they are leaving and not to tell anyone they were there. The big girl asks why not, saying she knows the black girls will get into trouble. She threatens to tell on them.

Shortly after this, the white girls’ troop leader enters the bathroom and assures the girls that everything will be all right. All the girls start crying. Then the ranger comes, then Mrs. Margolin and Daphne. Mrs. Margolin tells the leader of Troop 909 that the girls will apologize and their parents will punish them. The white girls’ leader denies that her girls are mentally handicapped but admits they are “delayed learners.”

The black girls are speechless, while the Troop 909 leader is full of words and energy. She tells Mrs. Margolin that some of her girls are “echolalic,” which means they will repeat whatever they hear. (Echolalia, the repeating of the speech of others, is a severe communication disorder associated with childhood schizophrenia and intellectual disability.) So they might have used the racial slur, but it would not have been intentional. Arnetta points to a small girl and says it was she who used the word. The troop leader says that is impossible, since the girl never speaks. Arnetta then picks out another girl as the culprit, but Laurel thinks it very unlikely that this happy-looking girl would call anyone a “nigger.”

On the fourth morning, they board a bus to go home. The journey is quiet to begin with, but then the girls all try to silently imitate the expressions and mannerisms of the white girls, trying not to laugh too hard and attract the attention of Mrs. Margolin and Mrs. Hedy. Octavia wonders why they had to be stuck at camp with "retarded" girls. When Laurel starts to tell a story, Octavia tries to shut her up, but Daphne encourages Laurel to continue. Laurel tells her about an incident in a mall when she was there with her father. They saw a Mennonite family, dressed in their distinctive garb. Laurel’s father had told her that if someone asked the Mennonites to do something for the person, they would be compelled to do it, because it was part of their religion. Laurel’s father asked them to paint his porch, and the entire Mennonite family came and did so. Laurel’s father explained to her that he had asked them to do this because it would be the only time he would be able to see a white man on his knees doing something for a black man for free.

Laurel now understands why her father said that, although she does not agree with the sentiment. When Daphne asks if Laurel’s father had thanked the Mennonites, Laurel replies no, and she suddenly realizes that there is “something mean” in the world that she cannot stop.