Johanna is starting her first year of high school, and a new girl shows up in class: Mia, who is mysterious and self-confident. Although all the boys want to date her and all the girls want to be her best friend, Mia picks Johanna to talk to the most. The shy Johanna is flattered that Mia wants to be “besties”. Together, the girls start up something so exciting that Johanna feels liberated and very adult. But then, Mia comes up with a plan that leads the girls into more and more trouble, and ultimately turns their lives head over heels.