In a Louisiana nursing home in 1999, Paul Edgecomb (Greer) begins to cry while watching the film Top Hat. His elderly friend Elaine (Brent) shows concern for him and Paul tells her that the film reminded him of when he was a corrections officer in charge of Death Row inmates at Cold Mountain Penitentiary during the summer of 1935. The cell block Paul (Hanks) works in is called the "Green Mile" by the guards because the condemned prisoners walking to their execution are said to be walking "the last mile" to the electric chair. Here, it is a stretch of faded lime-green linoleum. The other guards include Brutus "Brutal" Howell (Morse), Harry Terwilliger (DeMunn), and Dean Stanton (Pepper).
One day, John Coffey (Duncan), a giant black man convicted of raping and killing two young white girls, arrives on death row. Coffey shows all the characteristics of being a "gentle giant": shy, soft-spoken, fearing darkness, and crying often. Soon enough, John reveals extraordinary powers by healing Paul's urinary tract infection and resurrecting a mouse. Later, he heals the terminally ill wife (Clarkson) of Warden Hal Moores (Cromwell) who had a brain tumor. When John is asked to explain his power, he merely says that he "took it back."
Percy Wetmore (Hutchison), a sadistic and unpopular guard, who is the nephew of the governor's wife, has recently begun working on the mile. Percy recognizes that the other officers dislike him and uses that to demand managing the next execution. After that, he promises he will transfer to an administrative post at a mental hospital. An agreement is made, but Percy then deliberately sabotages the execution. Instead of wetting the sponge used to conduct electricity and make executions quick and effective, he leaves it dry, causing inmate Eduard "Del" Delacroix's (Jeter) execution to malfunction dramatically.
Shortly before Del's execution, a violent prisoner named William "Wild Bill" Wharton (Rockwell) arrives, due to be executed for multiple murders committed during a robbery. At one point he seizes John's arm and John psychically senses that Wharton is the true killer of the two girls, the crime for which John was convicted and sentenced to death. John "takes back" the sickness in Hal's wife and regurgitates it into Percy, who then shoots Wharton to death and falls into a permanent catatonic state. Percy is then housed in the Briar Ridge Mental Hospital. In the wake of these events, Paul interrogates John, who says he "punished them bad men" and offers to show Paul what he saw. John takes Paul's hand stating that he has to give Paul "a part of himself" in order to see and imparts the visions of what he saw, of what really happened to the girls.
Paul asks John what he should do, if he should open the door and let John walk away. John tells him that he is ready to die because there is too much pain in the world, which he is aware of and sensitive to, stating that he is "rightly tired of the pain" and is ready to rest. For his last request on the night before his execution, John watches the film Top Hat. When John is put in the electric chair, he asks Paul not to put the traditional black hood over his head because he is afraid of the dark. Paul agrees, shakes his hand, and John is executed.
As Paul finishes his story, he notes that he requested a transfer to a youth detention center, where he spent the remainder of his career. Elaine questions his statement that he had a fully grown son at the time and Paul explains that he was 44 years old at the time of John's execution and that he is now 108 and still in excellent health. This is apparently a side effect of John giving a "part of himself" to Paul. Mr. Jingles, Del's mouse resurrected by John, is also still alive—but Paul believes his outliving all of his relatives and friends to be a punishment from God for having John executed. Paul explains he has deep thoughts about how "we each owe a death, there are no exceptions; but, Oh God, sometimes the Green Mile seems so long." Paul is left wondering, if Mr. Jingles has remained alive for all of this time being but a mouse, how long it will be before his own death
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