In the Maine small town of Castle Rock, school teacher Johnny Smith (Christopher Walken) takes his fiancée sweetheart Sarah (Brooke Adams) to an amusement park. On the roller coaster, he suffers a bad headache and tells her that he must go home to sleep it off. Sarah begs him to stay, but he declines saying: "some things are worth waiting for". As he drives home, a tanker jackknifes in front of him and he ploughs into it and black out.
Johnny wakes up at the Weizak Clinic. His parents Herb and Vera (Sean Sullivan and Jackie Burroughs) are shown in by Dr. Sam Weizak (Herbert Lom). They tell him that he has been in a coma for five years and Sarah has married another man. The distraught Johnny is inconsolable.
One day, as a nurse mops his brow he seizers her hand. He has a super-real vision of being trapped in a screaming girl's bedroom. He tells the nurse: "Amy needs your help." The nurse knows that Amy is her daughter's name, but puzzled why Johnny knows her. The nurse rushes home to find her house in flames, but her daughter is safe.
After a few weeks of physical therapy, Johnny is able to walk again with some difficulty. When Johnny gratefully takes Dr Weizak's hand, he is jolted by another vision. It is wartime with burning buildings, advancing tanks. A protesting young boy is lifted into a horse-drawn cart, leaving his mother behind. Johnny tells Weizak that his mother survived. Weizak says that it is impossible, but Johnny knows her name and address. Weizak checks it out and it's true, but he cannot bring himself to speak to his elderly mother. Weizak comes back and tells Johnny: "you're either in possession of a very new human ability... or a very old one."
Sarah comes to visit Johnny. Catching his stare, she asks him not to look at her that way. He says that he can't help it while Sarah says that it's been five years, but Johnny remembers it as yesterday. She says that she now has a five-year-old son, named Denny. Johnny takes it well. She tells him that his power of "second sight" is the talk of the town. Against Weizak's advice, Johnny gives a press conference to defuse the situation. Cynical TV reporter Dardis (Peter Dvorsky) demands a demonstration. Aware that he is being mocked, Johnny takes his hand and says "You wanna know why your sister killed herself?" Taken off guard, Dardis calls Johnny a freak. Johnny's distressed parents watch the event on their TV and his mother collapses. At the hospital, Johnny holds her hand as she dies.
Johnny moves in with his father. A few days later, Sheriff Bannerman (Tom Skerritt) pays him a visit for his help to catch a serial killer known as the "Castle Rock killer". Johnny refuses. When Herb tells Johnny that he should use his power he's been blessed with, Johnny becomes furious. He thinks that his power is a curse, not a gift. One day, Sarah brings her son over when Herb is out. She puts Denny to bed and says: "haven't we waited long enough?" They finally have sex for the first time in five years.
After watching another TV program about the Castle Rock killer, Johnny calls Sheriff Bannerman and agrees to help. Bannerman and Officer Dodd (Nicholas Campbell) take him to the scene of the latest murder, but Johnny gets nothing. Bannerman is called to another murder scene at the park bandstand where there is a woman's frozen corpse. Dodd identifies the woman as Alma Frechette. John takes the dead woman's hand and instantly "sees" a man calling to her from the bandstand. "She knows him" says Johnny. He watches helplessly as she is killed with a pair of scissors. The killer is revealed to be Dodd. As Bannerman calls for him, but he leaves in his squad car. At Dodd's house, Johnny arrives where his mother tries to prevent him from entering. Johnny takes her by the arm and sees that she knew her son was the killer all along and she has been protecting him. Mrs. Dodd calls Johnny a devil, sent from hell, and that her son has been killing all "dirty women" in Castle Rock for their sins at her own encouragement. In an upstairs bathroom, Dodd impales himself on the scissors just as Johnny forces himself into the room. Dodd's equally deranged mother takes his gun and shoots Johnny in his shoulder. Sheriff Bannerman runs is and is forced to shoot and kill her to save Johnny's life.
Following this close brush with death, Johnny moves out of town to a remote cabin. His bullet injury eventually heals, but his headaches are getting worse. He takes private tutoring jobs, and he is persuades by millionaire Roger Stuart (Anthony Zerbe) to teach his introverted son Chris. Johnny arrives at the Stuart mansion as a loud and abrasive politician named Greg Stillson (Martin Sheen) is leaving. Johnny and Chris get along well, to Stuart's relief. Later, Johnny and Chris watch TV coverage to Stillson's campaign for state senator. Stuart says that Stillson is probably a liar and dangerous.
In a local newspaper office, editor Brenner is confronted by Stillson and his henchman/sidekick Sonny who demand that he retreat an anti-Stillson editorial in the next edition. Producing photographs of Brenner with a young woman, they threaten to "take his head off" if he doesn't do as they say.
At one of Johnny's tutoring session with Chris, he gets interrupted by a knock on the front door and it is Sarah whom is a Stillson campaign volunteer bringing him a brochure to vote for Stillson. Another man appears at the door and Sarah introduces him as Walt, her husband. After an uneasy introduction, they leave and Johnny breaks down. As Chris hugs him for comfort, Johnny has another vision of kids in hockey uniforms and falling through the ice of a frozen lake. One of them is Chris. Johnny goes to Stuart and insists he call off the kids ice hockey practice, or they'll drown. Stuart angrily fires Johnny despite Chris' pleas. The next day at a local news stand, Johnny reads a headline about two boys drowning in a skating accident. He calls Stuart's house, hanging up in relief when Chris answers. Apparently he heeded Johnny's warning not to go ice staking.
Meanwhile, Stillson's next rally takes place in a park opposite Johnny's house. Looking for Sarah, Johnny finds himself in Stillson's path. As they shake hands, another vision strikes: at Camp David, President Stillson orders a general to co-authorize an all-out nuclear missile launch against the USSR and the entire world which will bring on Armageddon. Stillson is shaken by Johnny's grasp, until Sonny pushes Johnny away.
Johnny goes to Dr. Weizak where he asks him that if he could go back in time knowing what he knows, would he kill Adolph Hitler? Weizak answers affirmatively. He thinks that the "dead zone" in Johnny's visions means that as well as seeing the future, he can also change it.
Seeing he must kill Stillson before he becomes President of the USA and brings on the end of the world through nuclear war, Johnny packs up his hunting rifle and takes a bus to the Castle Rock Civic Hall. He breaks into the hall where Stillson will appears the next day and lies in wait on the balcony with the rifle. As the hall fills, the charismatic Stillson arrives and invites Sarah and Denny onto the stage with him as he gives his speech. On the balcony, Johnny rises and takes aim. Sarah sees him and screams and as a result the shot misses. As the spectators panic and fleet the hall, the equally panicked Stillson snatches Denny from Sarah and uses him as a shield. John hesitates to fire again, and gets shot by Sonny and other security detail. Johnny falls from the balcony and lands on the floor onto some chairs. A youth photographs it all before running out of the hall. Paranoid as always, Stillson walks up and grabs Johnny after recognizing him from a few days ago and demands to tell him who hired him.
Johnny grabs Stillson's wrist and has a final vision where he sees a drunken and distraught Stillson in his office where there is a Newsweek magazine on his desk with the front cover of the photo of Stillson using Denny as a shield with the headline "No Future For Stillson". Beside the Newsweek magazine are other magazines and newspaper headlines with the same photo describing Stillson's cowardice. Stillston takes a gun from his desk and commits suicide. Johnny smirks at Stillson and weakly says: "It's over. You're finished." Stillson orders Sonny and the rest of his men to run out and find the youth who took the photos, leaving the hall empty except for Sarah and Denny. Johnny tells Sarah that his mission is accomplished and then dies.