Sister Johanna is sent by the Vatican to investigate allegations of misconduct at a Catholic school in Iceland. During her time there, a young student at the school watches the school's headmaster, Father August Franz, fall to his death from the church tower. Two decades later, the child—now a grown man—calls the nun back to the scene of the crime. Leaving her convent in France, Johanna has no choice but to make a trip to Iceland again, and even while reckoning with the mystery of Franz's death and the abuses of power that may have brought it on, she looks for the significance of her life-changing friendship with a girl she met years ago in Paris.