In 1954, seven-year-old Cathleen Harris is introduced to Catholicism by her agnostic mother (Julianne Nicholson) and is drawn in the faith. At 12, a shy and reserved Cathleen is offered a scholarship and enrolls in a newly-opened Catholic school, to where she claims to have felt the presence of God. At 17, to her mother’s dismay, Cathleen (Margaret Qualley) pursues a vocation as a nun, claiming to have earned a religious calling.
Cathleen enters a Catholic convent as a postulant under the tutelage of the Reverend Mother (Melissa Leo).In the convent she meets fellow nuns Sister Evelyn (Morgan Saylor), Sister Emily (Liana Liberato), and Sister Margaret (Ashley Bell), all of whom suffer from sexual urges during consecration. Meanwhile, the Reverend Mother becomes alarmed with the planned reforms of the Second Vatican Council, terrified that changes the archbishop insists upon will destroy the community that has been the home for these women their entire adult lives.