Answer:
The prologue wastes no time telling us that the narrator, Leo Borlock, is attracted to the unusual in our world. This becomes clear when he tells us about his love of porcupine ties. Through this seemingly small detail about him, a whole series of spectacular events is placed in motion. Leo's mother places a birthday announcement in the paper for him when he turns fourteen that tells of his penchant for the porcupines. Little did he know till much, much later that Stargirl Caraway, a most unusual and fascinating young lady, would read this and send an unsigned gift to him. This is the first of many mysteries that Stargirl brings to Leo's life and to the lives of all the other people lucky enough to be around her.
Fast-forward a few years. Stargirl, who up till now has been homeschooled, starts school at Mica High as a tenth grader, where Leo is starting his eleventh grade year. Stargirl's entrance to school is a Big Deal for all the students in this small Arizona town. She immediately starts a stir with her wacky outfits and even more wacky behavior. She does all sorts of stuff that students at Mica High just don't get. Most importantly, she's friendly all the time, even though no one seems friendly back. We can sum her up the same way the older, scholarly gentleman, Archie, affectionately calls her: she's a "rara avis," which translates into "rare bird." Word.
Stargirl continues to take the school by storm. The students are slow to warm up to her; she is nothing like they have experienced before. Hillari Kimble, for one, is totally determined to destroy any chances she has at making friends. However, a few things fall together for Stargirl, and after a very entertaining incident at a football game, she joins the cheerleading squad. Bingo. She's in. Suddenly, she's popular, and Leo's thoughts become more and more consumed with her.
But the dream can't last forever, folks. Her enthusiastic cheerleading, which made her popular in the first place, eventually leads to Stargirl's downfall. She cheers for everyone, in every situation, not just her home team. And while the students are happy with her upbeat kindness when it's aimed at them, they totally turn on her when her kindness extends to a member of the opposing team. Her fall from popularity is fast and ruthless. Everyone stops talking to her with the exception of two people: her one loyal friend, Dori Dilson, and Leo, who is too dizzy in love to see what's really going on.
When Leo emerges a bit from his foggy love-haze, he realizes the full extent of the shunning and also realizes that he is a target, too. Yikes. This thrusts him smack-dab in the middle of an internal conflict that continues for much of the rest of the novel. He needs to decide who he cares about more: Stargirl or everyone else? He continues to stand by her side, but breaks down one day and tells her how bummed he is now that everyone hates him. He tells her that she has to change in order for them to stay together. Stargirl cries, and then just like that, she disappears.
Susan, the former Stargirl, emerges and tries to become normal to please Leo. Leo eagerly takes on the role of coach, training her to be like everyone else. We don't know about you, but Shmoop smells trouble. Soon it becomes clear that the students do not accept her any better now that she is dressing and behaving more like them. Eventually, she chucks the whole normal plan and embraces her true identity, and Stargirl shows up again the next day.
Leo is ticked, and Stargirl knows it. She accepts the fact that he cannot love her for who she is, and tells him that she's cool if he doesn't invite her to the upcoming dance, so Leo doesn't go at all. Stargirl goes to the ball by herself, looking stunning as usual, and has a blast. Suddenly, the shunning is over. Suddenly, she is the Queen Bee again, leading everyone in a rousing rendition of the bunny hop.
Things are looking up for Stargirl, right? Wrong. After the ball, Stargirl disappears. Nevertheless, her brief time at Mica High has left a lasting impression on Leo and the other students. Mica will never be the same.