In a children's internment camp, the wristbands of many youngsters begin to beep, telling them to prepare for experiments that involve using their minds to try to collapse a giant tower at the center of the universe. Meanwhile in New York, eleven-year-old Jake wakes up after having nightmares, discovering that there has been an earthquake in the city. Jake often draws his dreams and among them are scenes of tortured children, wastelands and some humanoid figures. His parents send him to the shrink, complaining that there has not been much progress in the sessions. A classmate bothers Jake at school by taking his sketchbook, and Jake lunges at him without a second thought, separated by a teacher. Jake talks to the student counselor, who tells him that he can't tell the difference between reality and dreams. The boy insists that they are not dreams and that a man in black tortures children to bring down a tower along with beings in fake human skins.
According to Jake, if the tower collapses the world will be plunged into darkness and fire, but the counselor thinks these outbursts are due to the loss of his biological father over a fire saving people as a fireman. On the streets Jake notices a passerby whose face looks droopy as if he is wearing a mask, but before he can see any further a homeless man warns him that people are looking for special children like him for dark experiments. Jake manages to get on a bus and rides away only to meet his friend and neighbor Timmy. They go to Jake's apartment and find his mother and stepfather arguing about him and his attitude at school. They suggest to Jake the idea of going to a psychiatric boarding clinic for young people, something that upsets the boy.
At night Jake remembers the brave sacrifice his father made as a firefighter, and decides to put aside the nightmares issue. He puts away his drawings and goes to sleep and then enters the dream world, where he continues to have visions of the man in black. At the same time, two Gunslingers try to confront the man in black, but one of them falls. The younger one, Roland, is able to suppress the Man in Black's magic but is still no match for him. Jake wakes up and tells Timmy about the Gunslinger and how there’s a residence in New York that has something to do with him, but his friend doesn't believe him and leaves him to confront a social worker at the psychiatric clinic in his living room. Jake notices something strange and realizes that both the woman and her driver have markings similar to the fake creatures in the dream world, so he asks his mother to help him pack in private.
He unsuccessfully comments to her about the bad people, but neither his mother nor his stepfather believe him. Just before leaving, he manages to see that on the internet someone tells him the address of the possible home of the Gunslinger’s house, so Jake agrees to cooperate with the situation. He asks those present for a few seconds to look for his toothbrush but takes advantage of this to escape through the window. The driver chases him across the rooftops of the buildings, but Jake manages to make a fast forward and go down to the subway, losing sight of them. Jake talks to his mom on the phone and tells her he has things to do, until he arrives at the supposed house of the Gunslinger. Upon entering Jake manages to see some sort of gate with a control panel, he enters the same number he always dreams of, "1919" and the computer tells him the destination will now be Mid-World.
A portal opens next to Jake, and just before he steps through it, the floor of the house crushes away from itself and traps him. To free himself, Jake manages to enter the portal and reaches a desert world with no civilizations around, and with peculiarly shaped hurricanes in the distance. The man in black arrives at his facility and his workers tell him that there has been unauthorized access at one of the portals, being from the same boy they are trying to capture. Jake spends all night walking in the desert until he finds a small light in the distance, and when he arrives he finds an unlit campfire along with some water. As Jake drinks it, the Gunslinger appears from behind and points a gun at him, scaring the kid. Jake explains that he has dreamed about him, and although he tries to persuade him, the Gunslinger has no time for his explanations and leaves. When Jake mentions the Man in Black, Roland almost throws him off a cliff, thinking it is a trap. Jake explains that he knows his name is Roland and that he does not know the whereabouts of the Man in Black.
Roland believes him and explains to Jake that the Man in Black is a sorcerer and that his real name is Walter. The Man in Black goes to the human world and sees that the demon house has been destroyed by a powerful psychic. When he seeks answers from one of his henchmen, they tell him that only a human kid with a powerful Shine could have dealt with the house, something that leaves Walter perplexed. Roland and Jake make their way to a forest where they see the remains of an abandoned amusement park. They encounter a group of Taheens in the distance, who are Walter's henchmen, so they hide and go for a safer place to stay. Roland manages to prepare dinner and tells Jake that he doesn't know what the facilities around them are all about, with the boy explaining that they are themed parks.
They talk more about the confrontations Roland and Walter have had in the past, and how the last one they had involved the loss of Roland’s father. Walter goes to the workers of the so-called psychiatric clinic, berating them for losing Jake. He then instructs them to destroy each other and walks away, leaving his workers struggling in the street because of his magic. Jake draws a map where the dark tower is located in the center of the universe, surrounded by thousands of worlds. Roland explains that the tower is the only thing protecting the universe from infinite darkness and monsters, with Walter wanting to destroy it so he can rule in the new dark world. Jake proposes they work together to stop Walter, but Roland is reluctant to have a partner.
In the middle of the night they see a beam of light head towards the tower, with one of the children being used in Walter's facility. A voice calls Jake as he sleeps, causing him to march into the forest where he finds his father. Roland runs to save him knowing that it is a trap, and when Jake touches his father, a dark wall appears and tries to unleash a monster. Roland confronts it and stands up to it, but the wall takes on the appearance of his own father. Still Roland lunges at it and the wall disappears. The gunslinger tells Jake that it is a sign of the darkness that Walter is trying to pass into that world, and that their fathers were never really there with them. Believing themselves safe, they encounter a new dark creature, which manages to subdue Roland easily.
Jake takes the beast to the amusement park, trying to distract it while Roland manages to escape and lashes out at the creature and destroys it. Roland praises Jake's bravery, but Jake only notices how Roland is injured. Walter sneaks into Jake's house, and manages to control his parents to tell him where the drawings are, reproaching them for their poor treatment of the boy. Roland and Jake arrive in a village, where Roland's wounds are treated and they tells them about Jake's visions. There they mention how Jake's Shine is unique and very powerful, even able to read other people's minds. The seer Arra manages to make a connection with Jake, seeing that Walter's lair is in the northern wastelands, nearly six months' journey away. Jake mentions how the portals can get them there faster since Walter's minions are always looking for children from other worlds with them. They demand to use the village portal and although some object, they say that the law is to never oppose a gunslinger, so they decide to help them. Arra reveals that Roland's soul is actually in Walter's possession and that he can no longer be classified as a gunslinger. Roland confesses that even though everything is true, they must still try to defend the tower at all costs.
He leaves the place and notices that his wounds are getting worse and worse. Jake in turn tells the people that Roland is a good person and should still be treated as a Gunslinger. Although the technology is old, the portal seems to work well, so they both get ready to go. Just before that the town begins to be attacked by Walter's henchmen, who set fire to and destroy everything around. Jake helps a girl escape from the henchmen, while Roland defends the rest of the town but has complications from his injuries. Arra rescues him but they lose track of Jake, so Roland takes a slight break in the middle of town, to reflect on his feet. Arra doesn't understand what's going on, but after a few moments Roland shoots into the distance, managing to hit the guy who was kidnapping Jake. Roland tells them not to worry about them, as the longer Jake is there, the more danger they will be in, so the pair pass through the portal to Jake’s Earth.
Roland feels overwhelmed by everything around him, and Jake tells him that they should get him medical help immediately. However things are complicated by Roland's inexperience in the human world, as the doctors tell him that he actually suffers from too many ailments to let him go. They still leave, and Jake gives Roland painkillers and soda to make it better, with Roland saying he hasn't felt this good in years. Walter appears to Arra, manipulating her to tell her where Roland and Jake are, so he decides to go to Keystone Earth to follow them. Jake has the idea to ask the homeless man from earlier about the situation, but the man tells him that he lost his Shine years ago, so Jake must use his powers to read the man's memories. They decide to go all the way to Jake's house, but there they find his stepfather unconscious on the floor and a black burnt stain in the boy's room, thinking his mother perished to the man in black.
This is for Jake to use his Shine so they can track him, so Roland tells him he should close his mind and let the pain flow. On the terrace Roland promises the boy that he will personally take care of Walter himself as revenge for the two of them. He tells him that he hasn't recited Gunslinger's Creed in years, and teaches it to him as they practice aiming with tin cans. They go to an armory store and get their hands on enough materials, but Walter separates them, leaving Roland trapped in the store with him while Jake flees from his henchmen. Walter insults and annoys Roland by telling him that no matter how hard he tries, everyone who walks by him will perish.
Jake is kidnapped, but uses his Shine to communicate with Roland. They blindfold the boy so he won't reveal the location, but Roland still manages to find him, eliminating those in his path. They open a new portal to Walter and Roland's world, and Roland sees how the man in black has the boy subdued. Despite being surrounded by dozens of members, the Gunslinger manages to break through against them all. Walter and Jake go through the portal and Jake is forced to settle into the mind-draining machine, knowing that he alone has the power to bring down the dark tower with no trouble. The gunslinger uses all his weaponry to break through, regardless of the minions being armed and coming out all over the place. He uses all the weaponry he managed to take from the store and manages to shoot straight at everyone present. With the help of gas canisters, he causes an explosion that buys him some time. The computer indicates that there are problems with Jake's power as he is resisting and holding back, and Walter takes it upon himself to discourage him from losing his spirit, claiming that the gunslinger only cares about Jake so he can confront his nemesis. The boy is upset at the loss of his mom, and it's enough to trigger the light beam to the tower.
Roland confronts one of Walter's closest henchmen, and ends up on the streets watching the sky turn red and the earthquakes begin. A car takes out Walter's henchman and Roland is free to go with Jake. Seeing that Jake now has more power than ever to destroy the tower, Walter decides to buy time by confronting Roland. The man in black uses his powers to confront Roland, even driving a piece of glass into one of his hands and leaving the Gunslinger with only one hand available. Still Roland puts up a fight against Walter, with the villain managing to clip all of his bullets out of the air. Jake attempts to contact Roland mentally before Walter delivers the coup de grace, reciting the Gunslinger's Creed. Roland manages to launch two bullets that cross paths, changing direction just in time for one to hit Walter's heart. The Gunslinger manages to rescue Jake and destroys the machine, saving not only the tower but the entire universe.
They both see the city trying to cope with the recent catastrophes, with newscasts mentioning how everything is slowly returning to normal. They share some hot dogs and the Gunslinger asks Jake if he wants to go with him to his world, as there is nothing left for him there. The boy is thrilled and says yes, now being the Gunslinger's new ward.