From the relative tranquility of his nursing home (“Georgia Pines”), Paul Edgecombe recounts his time as death-row supervisor of Cold Mountain Penitentiary in 1932. As his narrative shifts back and forth between 1932 and the present, Paul explains that his goal in recounting this earlier period of his life is to provide a detailed account of one time during his career when he had serious doubts about his job.
At Cold Mountain, Paul supervises E block—the equivalent of what is commonly known as death row. E block has the nickname “the Green Mile” because of the color of the tiles in the long corridor leading up to the electric chair, where condemned inmates await executions in their cells. Paul believes in showing compassion toward the death-row prisoners. He and his colleagues Brutal, Harry, and Dean are constantly frustrated by the behavior of Percy Wetmore, a young guard who behaves cruelly toward the inmates, making the atmosphere on E block violent and unpredictable.
After the execution of The Chief (a Native American convicted for drunkenly killing a man in a fight) and the transfer of The Pres (who murdered his father by throwing him out of a window) to another section of prison, Eduard Delacroix arrives on E block. His arrival is marked by chaos and brutality, as Percy violently drags him into the corridor, insults him, and hits him with his baton. Paul scolds Percy for his behavior, but the young man, who trusts that his political connections can protect him in any situation, feels no sense of remorse—developing, instead, a growing hatred toward Delacroix.
One evening, when Delacroix is heard laughing in his cell, the guards discover that he is playing with a mouse that appeared on E block a few weeks earlier. At the time of the mouse’s first appearance, the rodent had amazed the guards with its quasi-human intelligence, having shown signs that it was looking for someone. Paul later realizes the mouse had been looking for none other than Eduard Delacroix. The mouse, whom Delacroix calls Mr. Jingles, becomes the inmate’s faithful pet and entertains the guards with various tricks. In particular, Mr. Jingles enjoys running after a wooden spool that Delacroix hits against his cell’s wall.
A few weeks later, John Coffey arrives on E block. Paul describes him as a giant—a towering black man who makes everything around him appear ridiculously small. After giving Coffey the usual speech he reserves for new inmates, Paul realizes that Coffey is soft-spoken and almost completely illiterate. Paul is startled by the peaceful gentleness that emanates from Coffey’s eyes, a strange tranquility that makes the man look absent and lost.
Spurred by a curiosity that later turns into an obsession, Paul searches for details about John Coffey’s crime. He discovers that Coffey was charged with the rape and murder of two nine-year-old girls, the Detterick twins. One summer morning, the two girls, who had been sleeping out on their porch, are found missing, the family dog strangled to death. A search party is called to look for the two girls, and the searchers ultimately find John Coffey holding the bloodied, dead bodies of the Detterick twins, whose heads have been smashed together. Crying ceaselessly, moved by desperation and grief, Coffey’s attitude appears to be a clear indication of guilt. Coffey is soon arrested and swiftly sentenced to death for his crime.
In the meantime, a young new inmate arrives on E block: William Wharton, a cruel murderer who plays violent tricks on the guards with a persistence that Paul finds terrifying. Wharton is often punished for his actions, forced into a straitjacket and confined to the restraint room for a few days, but never modifies his behavior.
The same day as Wharton’s arrival, Coffey urgently calls Paul into his cell, saying he needs to talk to him. Paul, who has been suffering from an excruciatingly painful urinary infection, sits down on Coffey’s bunk and Coffey suddenly touches Paul’s groin, sending a flow of painless energy through Paul’s body. After Coffey coughs up a cloud of black insects that turn white and vanish, Paul stands up and realizes that his urinary infection is entirely gone.
Coffey performs a second miraculous healing a few weeks later, on the day of Delacroix’s execution. When Delacroix throws Mr. Jingles’s spool against the wall a bit too hard, causing Mr. Jingles to exit the cell, Percy takes the opportunity to violently crush the mouse under his shoe. A few seconds later, from within his cell, Coffey tells Paul to give him the mouse. Paul hands it to him and the inmate holds the mouse inside his hands, breathes in, releases a cloud of black insects that turn white and disappear. The next moment, Mr. Jingles emerges from Coffey’s hands alive and well. The guards look on, utterly dumbfounded.
That same night, Percy takes his greatest revenge on Delacroix. He intentionally sabotages Delacroix’s execution, failing to wet the sponge that is typically used to conduct electricity through the condemned man’s head. As a result, Delacroix suffers an agonizing, minutes-long death on the electric chair during which he essentially burns alive. Furious about Percy’s loathsome action, the guards make Percy promise to apply to transfer to a job at Briar Ridge psychiatric hospital the next day, so that they might be rid of him.
In order to atone for Delacroix’s horrific death, Paul decides to use John Coffey’s powers to perform a good deed. He convinces Brutal, Harry, and Dean to take part in an expedition to heal the warden’s wife, Melinda Moores, of her recently diagnosed brain cancer. After sedating William Wharton with a strong drug and locking Percy up in the restraint room, the men drive John Coffey to warden Moores’s house. There, Coffey heals Melinda in the same way he previously healed Paul and Mr. Jingles. This time, however, Coffey is unable to cough up the black insects, and the guards notice that he begins to suffer from the same symptoms of which he relieved Melinda.
The guards successfully return to prison, bringing a weakened Coffey back to his cell, and let Percy out of the restraint room. However, before Percy has a chance to leave the Green Mile, Coffey suddenly grabs him through the bars of his cell. He forces Percy’s lips against his and transfers to him the illness that he had absorbed from Melinda Moores. Percy’s eyes go blank and, after taking a few uncertain steps, he suddenly shoots into William Wharton’s cell multiple times, killing the sedated inmate in his sleep. Percy never regains his sanity but, instead, is sent as a patient to the psychiatric hospital where he had applied to work.
As the official investigation surrounding Wharton’s death comes to an end and the date of Coffey’s execution approaches, Paul conducts an investigation of his own that leads him to confirm his long-held suspicion that Coffey is innocent. In the process, he discovers that William Wharton is the true rapist and murderer of the Detterick girls. John Coffey later confirms this fact, telling Paul that once, when Wharton grabbed John’s arm, John was able to see inside Wharton’s mind and learn about what Wharton did to the Detterick twins. The discovery of Wharton’s guilt is what spurred Coffey to make Percy kill Wharton on E block.
Disturbed by the idea of executing an innocent man, Paul reveals what he has learned to his wife (Janice) and colleagues. However, faced with the fact that it would be impossible to justify Coffey’s innocence without referring to his special powers (in addition to the fact that the racist justice system would never agree to re-open the case of a black man convicted of murder), Paul and his friends are forced to recognize that they will not be able to save Coffey’s life. The guards must thus prepare for Coffey’s execution with heavy hearts, feeling shameful for executing an innocent man with God-given healing powers. Coffey, however, claims that he is happy to die so that he may escape the cruelties of the world. Paul’s account of 1932 ends with John Coffey’s death on the electric chair—the very last execution of his career.
Once Paul finishes writing down his narrative at the nursing home, he shows his story to his special friend Elaine Connelly. He then brings her to a secret shed in the woods where he shows her Mr. Jingles, who is still alive. He explains that when Coffey touched Mr. Jingles, he made him resistant to the effects of aging. Paul also reveals that he himself is resistant to aging.
After Elaine dies a few months later, Paul is left to reflect on the difficulty of his present life. He recalls his wife Janice’s brutal death in a bus accident, during which he believes he saw Coffey’s ghost looking at him from a distance. At the nursing home, Paul feels alone in the world, left only with the memories of those he has loved and lost. While he knows that everyone is bound to die, he laments his current state, in which he must wait joylessly for his own death, as though this life were but a longer version of the Green Mile.