A wealthy young woman, Anne-Marie Lamaury, decides to follow her vocation and becomes a nun in a convent which occupies itself with the rehabilitation of female prisoners. During a prison visit, she meets another young woman, Thérèse, with whom she starts to take an interest. Thérèse resolutely claims that she is innocent and rejects Anne-Marie's attentions. When she is released from prison, Thérèse kills the man who committed the crime for which she was sentenced. She then seeks sanctuary in Anne-Marie's convent but is unable to speak about what she has done. Anne-Marie is nonetheless determined to bring about Thérèse's spiritual transformation, even if she risks alienating herself from her fellow sisters.