Briefly, the film is a Depression-era story about a seven-foot-tall black man named John Coffey (Michael Clarke Duncan) who is sentenced to death for the rape and murder of two small girls in a Southern town. Paul Edgecomb (Tom Hanks) is the head guard on the prison hallway, nicknamed "the green mile" for the color of its floor and the finality of its destination, where men sentenced to death spend their final days. All of the inmates under Edgecomb's watch (with the exception of Sam Rockwell's "Wild Bill" Wharton) seem surprisingly sedate and innocuous, but John Coffey, who cannot sleep without nightlights and seems forever on the verge of tears, is characterized so preciously that we cannot doubt he will be exonerated—to us, if not to the penal system—of the crimes he is alleged to have committed. Moreover, as high school English teachers never tire of observing, the innocence of martyred fictional characters bearing the initials "JC" must never be questioned. Indeed, as we first discover about an hour into The Green Mile, this particular JC bears mysterious powers of healing, as well as monumental capacities for sympathy and forgiveness, that make his Biblical heritage even harder to ignore or, for filmgoers who prefer not to be beaten over the head, to put up with.
Stated compactly, and sorry if it spoils a little bit of plot, the final two hours of The Green Mile find Coffey healing three characters—Paul Edgecomb, the warden's terminally ill wife (played my High Art's luminous Patricia Clarkson), and the pet mouse of a fellow inmate—from various states of disease before he is finally put to death in the electric chair. By that point, Edgecomb has offered Coffey in exchange for his good deeds the chance to escape both prison and certain death with the aid of the bewildered, admiring guards. Coffey declines their offer because, as he states, he wants to be put to death. The same powers that enable him to take away hurt from other people's (and mice's!) bodies require Coffey himself to live in a constant state of torment, feeling the pain of the world "like pieces of glass" inside his head. Executing Coffey, as King and director-screenwriter Frank Darabont would have it, comprises an act of mercy for a human subject whose whole, enormous body is shot through with the absorbed, amassed pain of the human race. Strangely, in the act of permitting Coffey to die, his powers for enduring and relieving pain, as well as a previously undisclosed gift for unnaturally long life, are communicated into the bodies of Edgecomb and, of course, the mouse, who have both lived for 100 years by the time we arrive in the Saving Private Ryan-style frame story, as emotionally cloying as it is formally unwieldy in a film that is already far too long.