Patricia and Isabel O'Sullivan arrive at St. Claire, a girls' boarding school, to study and settle into their new residence. There they encounter Alison, Wella, Catherine, and Doris, fellow students who also attend St. Claire, and they quickly bond over shared enthusiasm. Together the girls enjoy games and laughter for long periods, living in peace until Winfred enters—in a sudden and unexpected way—a gloomy, rude, and antisocial newcomer who inevitably brings trouble for the O'Sullivan sisters, their companions, and the entire community in the heart of campus.