Leo Borlock is an average student at Mica High School. He gets decent grades, is a member of the school's marching band and has always been content flying under the radar. But all that changes when he meets Stargirl Caraway, a confident and colorful new student with a penchant for the ukulele, who stands out in a crowd. She is kind, finds magic in the mundane and touches the lives of others with the simplest of gestures. Her eccentricities and infectious personality charm Leo and the student body, and she quickly goes from being ignored and ridiculed to accepted and praised, then back again, sending Leo on a rollercoaster ride of emotions.

When Stargirl's mother is hired as the costume designer on a movie, they relocate to L.A., where Stargirl quickly becomes involved with an eclectic assortment of characters.