1964, St. Nicholas in the Bronx. Father Flynn is a charismatic priest who is trying to upend the schools' strict customs, which have long been fiercely guarded by Sister Aloysius Beauvier. The Sister is the iron-gloved principal who believes in the power of fear and discipline. With the winds of political change, the school has just accepted its first black student, Donald Miller. But when Sister James shares with Sister Aloysius her suspicion that Father Flynn is paying too much personal attention to Donald, Sister Aloysius sets off on a personal crusade to unearth the truth and to expel Flynn from the school. Now, without any proof, besides her moral certainty, Sister Aloysius locks into a battle of wills with Father Flynn. This threatens to tear apart the community with its irrevocable consequence.