Nadine (Hailee Steinfeld) and Krista (Hayley Lu Richardson) are inseparable best friends attempting to navigate high school together...until Nadine discovers her older brother and Krista have been secretly dating behind her back. They soon realize that there is a fine line between best friends and worst enemies. The cast of the film is rounded out with Kyra Sedgwick, who plays Nadine's well-meaning but completely ineffective mother, and Woody Harrelson, who plays Mr. Bruner, Nadine's English teacher and mentor, who is uncannily wise in the ways of girl-clashes.