Matthew Poncelet has been in prison for six years, awaiting his execution by lethal injectionfor killing a teenage couple. Poncelet, located in the Lousisiana State Pernitentiary,committed the crimes with a man named Carl Vitello, who received life imprisonment. As the day of his execution comes closer and closer, Poncelet asks Sister Helen to help him with a final appeal.
She decides to visit him, and her expectation is that he will come across as arrogant, sexist, and recist, not even pretending to feel any kind of remorse. Instead he affirms his innocence, insisting it was Vitello who killed the two teenagers. Convincing an experienced attorney to take on Poncelet's case pro bono, Sister Helen tries to obtain life imprisonment for Poncelet. Over time, after many visits, she establishes a special relationship with him. At the same time, she gets to know Poncelet’s mother, Lucille, and the victims’ families. The families do not understand Sister Helen's efforts to help Poncelet, claiming she is "taking his side". Instead they desire "absolute justice", namely his life for the lives of their children.
Sister Helen’s application for a pardon is declined. Poncelet asks Sister Helen to be his spiritual advisor through the day of execution, and she agrees. Sister Helen tells Poncelet that his redemption is possible only if he takes responsibility for what he did. Just before he is taken from his cell, Poncelet admits to Sister Helen that he killed the boy and raped the girl. During his execution, he appeals to the boy's father for forgiveness and tells the girl's parents he hopes his death brings them peace. Poncelet is then executed and later given a proper burial. The murdered boy's father attends the ceremony and begins to pray with Sister Helen, ending the film.