In 1957, a homeless young pregnant woman named Mary runs away from her abusive father following the accidental death of her younger brother William. When her boyfriend Jimmy's band goes on tour, she chooses not to go with them and instead goes to a soup kitchen. There a nun offers her refuge in a convent where she must obey the strict rules of Mother Superior. When she attempts to leave the convent, they drug her and rename her "Agatha", locking her inside a coffin that they only open to feed her and reinforce their brainwashing.

At a "donor breakfast" where the girls are judged by the convent's donors Mary escapes from the house and runs aimlessly through the woods but falls and gets her arm caught in a bear trap. The Wrights, a donor couple, bring her back to the house, where Mother Superior commands her to put her wounded arm in saltwater as punishment.