A well-off young woman decides to become a nun, joining a convent that rehabilitates female prisoners. Through their program, she meets a woman named Thérèse who refuses any help because she says she was innocent of the crime she was convicted for. After being released from prison, Thérèse murders the actual perpetrator of the crime and comes to seek sanctuary in the convent.

An inexperienced, sickly priest shows up in the rural French community of Ambricourt, where he joins the community's clergy. But the locals don't take kindly to the priest, and his ascetic ways and unsociable demeanor make him an outcast. During Bible studies at the nearby girls school, he is continually mocked by his students. Then his attempt to intervene in a family feud backfires into a scandal. His failures, compounded with his declining health, begin to erode his faith.