The "Shawshank Prisoner" is a young man who is found locked in a hidden cell in a disused section of Shawshank State Penitentiary. In reality, he is the Henry Matthew Deaver of an alternate timeline, pulled into the current timeline after encountering the young Henry Deaver.
Henry Deaver is the biological son of Reverend Matthew Deaver and Ruth Deaver. As a child, Matthew used to take Henry into the woods to try and make him hear the Voice of God. Ruth began to fear for Henry, and told him to lie to Matthew and just tell him he heard it. Eventually, at the urging of Sheriff Alan Pangborn, Ruth left Matthew and took Henry with her.
The now adult Henry lives a normal life with his wife and they are trying to start a family. Due to Ruth suffering from early-onset Alzheimer's, Henry is a doctor trying to find a cure for the disease by using technological implants in the brain. After a presentation showing the effectiveness of his design on a cat, Henry receives a call from Alan Pangborn, who is living with his mother. His father, Matthew, has committed suicide.
Henry returns to Castle Rock, Maine to put his father's affairs in order. He reconnects with Molly Strand, and they spend time at The Mellow Tiger catching up. Returning to Matthew Deaver's house, Henry has to fix a broken fuse in the basement. Down there, he finds a young black child in a cage. Understandably shocked, Henry calls the police.
Officer Dennis Zalewski questions Henry about the boy, who only says the name "Henry Deaver." The boy tries to run away into the woods, but is caught and taken away by the police. Henry begins to go through his father's belongings and finds a large number of audio tapes. Listening to them, he finds out where the boy came from. The boy appeared twenty-seven years previously and said that he was "Henry Deaver"; Matthew Deaver's adopted son. He was in the woods with his father trying to hear the Voice of God when something happened and Henry found himself elsewhere. Matthew tested the young Henry and his story checked out since he knew things that only his Henry would know. However, Matthew comes to believe that this Henry is a servant of the devil, sent to him when he wished for it. Matthew drugs the young Henry and keeps him in the basement for years. The young Henry never ages, and over time Matthew spends more time with him such as at Christmas, and teaches him to carve figures from soap like he taught Henry.
Henry tells Molly about everything, leading to them going to talk to the young Henry. Molly convinces the local sheriff to release the boy into their care. While driving home, Molly is gripped by the need to help the boy go towards the sound he hears. She speeds over the train tracks, and an oncoming train blocks Officer Zalewski's cruiser – who had been assigned to watch over them – long enough for Molly to get some distance between them.
The young Henry runs into the woods, followed by Molly and Henry. Officer Zalewski follows and Henry tries to calm the police officer down. Young Henry and Molly run deeper into the woods, followed by Henry and Zalewski. During the chase, Zalewski accidentally shoots and kills Molly. Henry holds Molly in his arms, and she tells him to help the boy. Suddenly, Henry finds himself in a space between worlds and follows the young Henry, emerging in the snowy surroundings of Castle Lake in 1991. From a bluff, he watches as Sheriff Alan Pangborn finally finds Henry after days of searching.
Trapped in the alternate Castle Rock
The prisoner was kept locked up by Warden Lacy in a cage in a water cistern below the disused Block F of Shawshank State Penitentiary. Shortly before Lacy committed suicide, he told the Prisoner that, when he was found, he should ask for "Henry Matthew Deaver."
Shawshank was sold to a private company, Northeast Correctional, and Lacy committed suicide on his last day as warden. The new warden, Theresa Porter, wanted to reopen Block F – which had been closed ever since a fire in the eighties killed a number of inmates – leading to the prisoner's discovery by guard Dennis Zalewski. The prisoner does not speak and appears timid, although he does mention Deaver's name.
Warden Porter decides to keep him imprisoned since there are no records about him, and hopes the situation will resolve itself by putting him in with a particular violent inmate. The prisoner soon manages to escape his cell, and Zalewski watched on monitors as he walked through the prison, the gates opening for him and with a number of dead guards in his wake.
However, the incident never occurred, and the prisoner was still in the infirmary. Zalewski went to see the prisoner and ask if he somehow left the prison the previous night although he got no answer. Warden Porter and her deputy warden, Reeves, decided to move the prisoner to share a cell with a Neo-Nazi prisoner, Garrett Coyne. The prisoner warned his new cellmate not to touch him; shortly after, Coyne was dead of cancer.
In an effort to get the prisoner's plight know, Henry and Zalewski conspire to get Henry access to the prisoner. While Henry joins the local congregation during their regular visit to the prison to administer to the prisoners, Zalewski gets the prisoner outside so that Henry can see him through the fence. Henry tells him that he will be his lawyer and takes a picture of him as proof before the prisoner is led back inside by guards.
After the existence of the Kid is revealed by Molly Strand live on air on the regional show "Local Color,"Henry Deaver meets with Warden Porter with a settlement offer of 300,000 dollars contingent on signing an NDA. Initially, Henry plans to tell his client not to take the deal, but personal events force him to reconsider staying in Castle Rock. Shortly after, Dennis Zalewski commits a mass shooting in Shawshank, seemingly influenced by the Kid after visiting him in a cell.
The scandals forces the prison to release the Kid. Feeling responsible, Henry arranges for him to stay in a room above Molly Strand's office while waiting for room at Juniper Hill Asylum. He fashions a cage to sleep in, then roams the neighborhood at night, spying on a birthday party that descends into violence. The next day, Jackie Torrance visits him and drives him around, talking and eventually getting high. The Kid then stands on top of the old shirt factory, seemingly to commit suicide, but is talked down by Molly Strand. Molly senses the wrongness in the Kid.
The Kid heads to Ruth Deaver's house, and Alan Pangborn is alerted to his presence through the use of an app linked to security cameras in the house. Alan tracks him down in the woods and confronts him, wondering why he has not aged. The Kid says that he can help Ruth. He sends Alan on a quest to find Warden Lacy's car, which is now at a junkyard in another town.
Eventually, the Kid's behaviour unnerves Henry, who gets him admitted to Juniper Hill. Shortly after, a fire is started at the asylum, killing several patients and staff, and allowing the prisoner to escape.
The Kid goes back to Ruth's house, and disorients her with his behavior. She has come to believe that he is Matthew Deaver resurrected, and that she has to protect herself. In the end, she kills Alan Pangborn be mistake.
After being in the Filter in Odin Branch's modified RV, Henry arrives back at his mother's house to find Ruth sleeping, no sign of Wendell, and the Kid in the kitchen. Henry confronts the prisoner about Wendell's location, but his son soon arrives. Henry tells him to look himself in a room upstairs while Henry and the Kid head to the garage.
In the aftermath of Ruth shooting Alan, the Kid attempted to protect her by cleaning up the crime scene so that Ruth would not be blamed for the murder. He tries to convince Henry of his plan, but Wendell already called the police because he was worried about the stranger in the house. The kid flees out of the back door, leaving Henry to face questioning.
However, the Kid does not go far, breaking into Molly Strand's parents house. That night, Molly is drawn to the house and is met by the Kid. He tells her things that he should not possibly be able to know, and then comments that the woods out back is where she died. He then tells her about himself – that he is an alternate Henry Matthew Deaver pulled into this world.
After telling Molly his story, he asks her to convince Henry to meet him at Harmony Hill Cemetery because he wants to show him something. Breaking into Theresa Porter's home, he leaves a carved soap figure for her before heading to the cemetery. He waits for Henry in front of a grave that marks Ruth and Matthew's stillborn son. However, Henry gives his location to police and he is arrested in connection with the Juniper Hill Asylum fire.
In the holding cells, he talks with Henry who is being held in connection with the death of Odin Branch. They are placed in the same cell when the police need to use the other cell to house prisoners from Shawshank State Prison who were being transported on a bus that then run over and killed Warden Porter. The alternate Henry seemingly causes the prisoners to riot and overpower the guards, allowing him to take Henry at gunpoint into the woods, searching for the way back to his own world. In the woods, Henry overpowers his alternate self, and in a flash sees his face aged and deformed.
One year later, the alternate Henry is back in the cage beneath the now-abandoned and shut down Shawshank. Henry brings him food and is now his captor. As Henry leaves, the prisoner smiles into the darkness.
Behind the scenes
- The Shawshank Prisoner is played by Bill Skarsgård. Some release materials refer to him as "The Kid," but it is unclear if he is meant to be the same character.