Astrid, the narrator, and protagonist of this graphic novel, begins by informing the reader that the story she is about to tell began back when she was still fifth-grade friends with her bestie named Nicole. Astrid's mother announces the three on are their way to the latest of her many attempts to provide the girls with an "evening of cultural enlightenment." Rather than modern art or the opera, however, the girls are amazed to be driven to the site of a local amusement park where they are introduced to the exciting sport of roller derby.
Although Nicole is a little intimidated by the power and potential violence of the spectacle, Astrid is captivated. The punny nicknames of the players alone are enough to stimulate Astrid's fascination. Two are called Scald Eagle and Scrappy-go-Lucky, for instance, but she is especially bewitched by a skater known as Rainbow Bite. Rainbow holds the key position of jammer for her team and her ability to score points ignites Astrid's desire to pursue the sport.
Hoping that Nicole is as captivated as she was by the sport, Astrid asks her best friend to come with her to roller derby camp. Nicole declines and in their absence from each other eventually becomes friends with a girl named Rachel who has always taken great delight in bullying Astrid. Meanwhile, at roller derby camp, Astrid also finds another friend, Zoey. Astrid's initial attempts at mastering just the basics of skating do not go well, and she considers giving up entirely. Realizing that Rainbow Bite's locker is near her own, she decides to leave a note asking the pro for some helpful advice. The words of encouragement with which Rainbow replies are all it takes to give Astrid the stimulation she needs to continue pursuing her dream.
In an attempt to further master her skills skating at high velocity, Astrid loses control while skating at great speed down a steep hill. It is only by remembering what she has been taught about the art of surviving a crash that she manages to avoid serious injury despite ending up head over heels in a bush. Having survived the crash by the putting theoretical technique of the "small fall" into practice, Astrid comes out of her near-disaster with a newfound sense of pride and accomplishment. This upbeat attitude is strengthened by ever more encouraging words from her teammates as well as developing a closer bond with Zoey.
This bond with Zoey reaches the point at which Astrid allows her new friend to dye her hair blue. The confidence also allows Astrid to improve her skills in the roller derby rink. This intensification of her game pushes Astrid to decide she wants to become a jammer like her hero, Rainbow Bite. Everything is going great until one day she accidentally eavesdrops on Nicole and Rachel talking about her. Astrid is not surprised to hear Rachel talking trash about her but is shocked to hear Nicole going along with it. Unable to control herself, she confronts them about their mean bullying but only succeeds in humiliating herself in front of her former best friend. Things continue to spiral downward when she learns that Zoey has been picked for the position of jammer on the team instead of her. This news also results in Astrid getting angry with the consequence of Zoey refusing to talk to her for a few weeks. Upon learning of the rift between her daughter and Nicole, Astrid's mother takes her daughter by the library every day after picking her up from the roller derby camp. Over this period, Astrid contemplates the events of the summer and decides to make amends.
On the day of the big derby match, Astrid asks Zoey to forgive her and proceeds to get everybody to cheer loudly for Zoey to help get past her nervousness. Upon seeing that Astrid has sincerely sought her forgiveness, Zoey accepts the apology, and the friendship is repaired. During the match, Astrid—now known by her derby nickname Asteroid—takes a massive hit and falls flat on her rear. Rather than being embarrassed, however, it turns out that taking the hit allows her team to score and win the match. Afterward, Nicole approaches Astrid with flowers, asking if she wants to join her and her family for dinner. Astrid graciously accepts the bouquet but decides she would rather celebrate with her teammates, thus effectively letting go of her former dependency upon Nicole.
Afterward, Astrid sees Rainbow Bite and introduces herself using the nickname she had used when asking for advice, Rose Dud. Rainbow autographs her program by writing that Astrid is a hero for being willing to take a hit for the team. She also adds a special note at the end, telling her that Asteroid is a much better name than Rose Dud.
The last panel shows Astrid surrounded by her new friends sitting at a circular table. Her words indicate that the opening lines inform the reader that the story began back when she was in fifth grade with her best friend being spoken to her friends and the whole book has her telling her friends "the story of roller derby fame."
