When Leo Borlock was a little boy, his uncle gave him a porcupine necktie. As a newcomer to Mica, Arizona, Leo decided to start a porcupine necktie collection. His collection is mentioned in a small newspaper feature on Leo’s 14th birthday. A few days later, Leo receives a package containing another porcupine necktie. The sender is a complete mystery.
On Leo’s first day of 11th grade, all of Mica High is whispering about a new 10th-grade girl named Stargirl Caraway. Stargirl wears flowing dresses and carries a ukulele on her back. Leo’s best friend, Kevin, tells him that Stargirl was homeschooled until recently. They make plans to interview Stargirl on Hot Seat, the student TV show they co-created. Over the coming days, Stargirl’s strange outfits—and her habit of serenading kids in the lunchroom—lead to speculations that she’s a fake. Stargirl also brings her pet rat, Cinnamon, to school and has an unsettling habit of greeting strangers in the hallways. Mica High is “not exactly a hotbed of nonconformity,” and Stargirl’s ways continue to baffle the other kids. Leo, however, decides there’s something wonderfully real about her, though he can’t pinpoint what it is.
A few weeks later, Stargirl shows up at the Mica High football game and thrills the normally dull crowd by dancing around the field. Soon after, the head cheerleader invites Stargirl to join the squad. Leo and Kevin ask the advice of Archie Brubaker, a retired paleontologist who mentors the kids of Mica. Archie admits that Stargirl is very different, but that he believes she’s closer to “who we really are.” He tells the boys that they’ll know Stargirl “more by your questions than by her answers.” By December, Stargirl has become the most popular kid in school. Both boys and girls—shy, popular, athletic, and nerdy kids alike—are drawn to her. Inspired by Stargirl’s kindness, kids start acknowledging and celebrating one another, and they express their individuality more in their dress, activities, and opinions. School spirit grows alongside the outburst of nonconformity. Leo looks back on this time as a “golden age” that wasn’t to last long.
Things change as the Mica High Electrons make the state basketball playoffs. Suddenly, Stargirl’s overenthusiastic, goofy cheering becomes threatening: she starts offering cheers for the opposing teams. When Stargirl is interviewed on Hot Seat, the student “jury” panel, led by Stargirl’s meanest detractor, Hillari Kimble, turns hostile. They start by criticizing Stargirl’s name and out-of-bounds cheering, and end by hurling accusations, claiming Stargirl just wants attention and demanding, “Why can’t you be normal?”
After Mica High is eliminated from the playoffs, Leo finds a childish valentine in one of his notebooks. It’s from Stargirl. Conflicted, Leo avoids Stargirl at first, but he’s helplessly drawn to her. Their first date is a walk in the desert, where Stargirl teaches Leo how to meditate. Leo is giddy with happiness about their relationship and is oblivious to much else. After a few days, though, Leo notices that the entire student body is shunning the two of them. Kevin explains that this is because they hold Stargirl responsible for sabotaging Mica High in the basketball tournament. When Leo seeks out Archie’s advice, Archie says that Stargirl seems to be in touch with a more primitive part of humanity that has become obscured in most people. He says the only question that matters is whose affection Leo values more: Stargirl’s or the other students’. Meanwhile, Leo and Stargirl go exploring together, and Stargirl teaches Leo how to see the beauty and magic in everyday things. He also helps Stargirl on her secret missions, delivering cards and gifts to strangers. He realizes that Stargirl was the sender of his porcupine necktie two years ago.
As much as Leo loves spending time with Stargirl, he is also tormented by his classmates’ shunning. He wishes he could have it both ways—Stargirl and his peers’ acceptance. He finally confronts Stargirl—doesn’t she care what everyone thinks of her? Stargirl is baffled by Leo’s instinctive connection to “everybody else”—something she realizes she lacks. Leo tries to explain the importance of going along with the group because, like it or not, “we live in a world of ‘them,’” and “they” don’t like Stargirl. A couple days later, Stargirl appears at school dressed in “normal” clothes, calling herself by her birth name, Susan. Leo is delighted and now enjoys being seen with her in public. But Susan’s desperate attempts to conform don’t win her classmates’ affection. But then Susan has a vision that she wins the state oratorical contest and receives a hero’s welcome, finally becoming popular. As she’d predicted, Susan’s oratorical performance is a resounding victory. But when they return to Mica High, nobody but two teachers and Susan’s friend Dori Dilson has shown up to cheer for her. At school the following Monday, Susan is Stargirl once again. She kisses Leo and tells him she’s given up on being normal. She also knows he won’t ask her to the upcoming Ocotillo Ball, and tells him it’s okay.
At the Ocotillo Ball, Stargirl shows up alone. She wears a regal outfit and joyfully dances solo. One guy finally asks Stargirl to dance, and not long after, she’s leading a line of students in a goofy version of the bunny hop. The long line of kids wanders off into the desert and returns, still dancing. The dance is remembered decades after the fact. Before Stargirl leaves, Hillari Kimble slaps Stargirl for “[ruining] everything,” but Stargirl just kisses her cheek in return. Nobody from Mica High sees Stargirl again. Later, Archie informs Leo that Stargirl has moved to Minnesota with her family. He shows Stargirl’s secret “office” for doing kindnesses to people to Leo: a toolshed filled with art supplies, a birthday calendar, and meticulous files on everybody at Mica High.
Fifteen years later, Leo is a set designer back East. Nowadays, Mica High has a “Sunflower Club” dedicated to good deeds, a ukulele player in the marching band, and a tradition of cheering for their opponents. Leo still thinks about Stargirl all the time and wonders if he’ll ever get another chance with her. But he doesn’t feel alone. Just before his most recent birthday, he received a porcupine necktie in the mail.