Sister Helen Prejean accepts an offer to become pen pals with a Death Row inmate named Pat Sonnier. She meets him, gets to know him, becomes his spiritual advisor, and starts to understand how flawed the system is. Pat had terrible legal representation, he may not even be legally eligible for the death penalty, and he feels genuine remorse for his crimes—but nothing Prejean does can save him. She is present when he is finally electrocuted.
Prejean becomes pen pals with and spiritual advisor to another, much less sympathetic inmate name Robert Lee Willie. Robert is harder for Prejean to deal with, but over time, these two also form a close bond. Although Robert seems like a pretty bad dude, he also shows potential for growth. His legal case also had tons of issues—but nothing can save him, either. Prejean watches as he is executed.
Prejean becomes a vocal opponent of the death penalty but also, partly inspired by her friendship with the Harveys (the mother and stepfather of Robert's victim Faith Hathaway) makes greater efforts to advocate for victims' rights. Her message is that all killing is wrong, and the system should be fixed to reflect that.