The head nun of St. Katherine's, known only as "Reverend Mother", objects to taking Deloris in but Monsignor O'Hara, who is the local parish priest, convinces her to go along with it because the police will pay the failing convent a good sum of money. Disguised as "Sister Mary Clarence", Deloris initially has difficulty dealing with the rigid and simple convent life but starts to befriend the other nuns, including the perky Sister Mary Patrick, the elderly Sister Mary Lazarus and the shy novice Sister Mary Robert. One night, after a poorly attended Sunday Mass, with a lackluster performance from the convent choir, led by Mary Lazarus, Deloris sneaks out to a bar, followed by Mary Patrick and Mary Robert. They are caught by the Reverend Mother, who orders that Deloris join the struggling choir. With her singing experience, Deloris is elected their director and she works to transform the choir.