Gertrude Baniszewski (Catherine Keener), a divorced mother of several children, agrees to take care of two girls, Sylvia (Ellen Page) and Jennie (Hayley McFarland), while their parents travel with a carnival. Though her eldest daughter is the real troublemaker, Gertrude vents all her bitterness and frustration on innocent Sylvia. Gertrude imprisons the girl in the basement and tortures her, eventually encouraging her children to follow suit.