Sister Helen Prejean teaches at Hope High School and works with the poor of New Orleans when Chava Colon, representing an organization known as the Prison Coalition, asks if she will become a pen pal with a prisoner. She agrees and is assigned to write to Elmo Patrick Sonnier, convicted of the murder of a teenage couple. Helen is young and excitable and sends off a picture of herself with her first letter to Patrick. She's somewhat surprised when he writes back and they correspond over the coming weeks until Helen broaches the subject of visiting. Patrick is excited at the prospect and names Helen his "spiritual advisor." She receives permission to visit him and isn't really prepared for the polite young man who does not seem like someone who would have committed the horrible crimes. Helen soon realizes that she needs to help Patrick with his legal battles as well and convinces attorney Millar Farmer to take the case. He does and begins working to prove that Patrick's initial legal defense was inadequate but is unable to prompt a stay of execution or a change of sentence through the courts the pardon board or the governor's office.

Helen learns through her experience with Patrick that the legal system is skewed in that wealthy people who can afford an experienced capital case attorney never get the death penalty and that capital punishment is more often meted out in cases with white victims than if the victim is black. This, along with her inner conviction that killing is wrong in any situation prompts Helen to throw her support into programs seeking to eliminate the death penalty. She vows she will never again serve as a personal advisor to a death row inmate but agrees to do just that when Millard Farmer calls and makes the request on behalf of Robert Lee Willie, convicted of the stabbing death of a young woman. Robert is very different from Patrick and Helen is somewhat tougher on him because she feels she was too lenient with Patrick. She reminds herself that she is supposed to be helping Robert prepare for death and that her job is to help him spiritually.

Helen, in her quest to fight the death penalty on principle, finds herself torn between dealing with the spiritual, legal and emotional needs of the convicted murders and the desires of the victims' families for revenge. She cites the toll a death plays on families, especially when the victim is a child. Parents often divorce as each tries to find a way to work through the grieving process. Helen argues that executing the convicted murderer makes those who pull the switch equal to the murderer. She says that the process is arranged so that everyone is able to say he was doing a job as ordered and has no personal responsibility. The problem with that, according to Helen, is that the system is flawed, those who are executed are likely to be poor and their victims white, and that justice is neither fair nor measured.