On the night of his retirement party, Reno police detective Jerry Black (Jack Nicholson) leaves the celebrations to visit a crime scene with detective Stan Krolak (Aaron Eckhart). He's just that kind of a guy — go figure. An eight-year-old girl has been found brutally stabbed to death. When no one else has the courage to tell the parents, Black volunteers. He makes a solemn pledge to the mother (Patricia Clarkson) on the cross of Jesus, which the little girl made, to find the murderer.

The police track down a retarded Native American (Benicio Del Toro) with a long rap sheet. He fits the description of a man seen fleeing the scene by the boy who found the body. After Krolak browbeats the suspect into a confession, the Indian steals a gun from one of his jailers and commits suicide. Everyone including Black's boss (Sam Shepard) is convinced that the case is closed.

Instead of heading off to Mexico on an all-expenses-paid fishing trip given to him by his coworkers, the intrepid workaholic starts his own investigation interviewing the little girl's grandmother (Vanessa Redgrave), a school classmate, and a cop (Costas Mandylor) in another town who worked on a similar case. When his superior rejects all the work he's done and asks why he's not enjoying his retirement, Black answers: "I made a promise. You're old enough to remember when that meant something."

Sean Penn directs this moody and pensive modern morality drama adapted from a 1958 novel by Swiss dramatist Friedrich Durrenmatt by Jerzy Kromolowski and Mary Olson-Kromolowski. Similar to The Indian Runner and The Crossing Guard, this character-driven film takes its time unfolding by paying special attention to the small details that signal dramatic changes in peoples' lives. Black, for instance, draws himself deeper into his investigation by purchasing a run-down gas station and rescuing Lori (Robin Wright Penn), a waitress with a young daughter the same age as the victim of the terrible crime. They move in with him after her husband beats her up again.

Black's obsession with the case intensifies as he zeroes in on a Christian fundamentalist who seems to have an unusual interest in little girls. The Pledge provides a rich psychological study of a man whose commitment to a promise does not turn him into a better man. Instead it sets him on a course that will eventually lead to a dark and angry and lonely place where he never wanted to be.