Twenty-seven years after their first encounter with the terrifying Pennywise, the Losers Club have grown up and moved away, until a devastating phone call brings them back.
27 years after the Losers Club defeated the evil clown Pennywise, IT has resurfaced and begun to claim more victims. Mike Hanlon, who never left the town of Derry, becomes aware of IT’s return, and he calls Bill Denbrough, Ben Hanscom, Beverly Marsh, Richie Tozier, Stanley Uris, and Eddie Kaspbrak to come back. All of the Losers return home, except for Stanley, who slits his wrists since he knows he cannot face Pennywise again.
Mike tells the Losers that they can kill Pennywise for good by performing an ancient ritual using artifacts from their childhood. The Losers split up and go around Derry to recover their personal artifacts, all while Pennywise attempts to get back inside their heads and torment them. Meanwhile, psycho bully Henry Bowers escapes from a mental institution to kill the Losers, but he is killed by Richie after an attack.
Bill fails to save a young boy from being a victim of Pennywise, so he and his friends prepare to kill IT once and for all. The ritual turns out to be a dud, and Pennywise takes on his true monstrous form to kill the Losers. They overcome their fears and fight back, but Pennywise fatally impales Eddie. The Losers then force Pennywise to believe that he is small and powerless, and they rip his heart out and destroy him.
The Losers split up once again and go back to their lives, now less afraid than before. Ben and Bev start a relationship, while Richie, who was in love with Eddie, honors his memory. Bill reads a letter that Stanley sent everyone in which he says he died to give the Losers a better chance to fight IT since he knew he was too afraid to go back himself. Mike also ends up leaving Derry for the first time to go see the world.
In 2016 Derry, Maine, Adrian Mellon is beaten and thrown from a bridge, then killed by Pennywise. Mike Hanlon overhears the incident on a police scanner and rushes to the scene. Upon realizing that It has resurfaced, he calls the other members of the Losers—Bill, Ben, Beverly, Richie, Eddie and Stan—back to Derry. All are amnesiac about their childhoods and disturbed by the calls, but agree to return. Stan, however, commits suicide. The remaining members reunite at a local restaurant, but the night goes horrifically when monstrous conjurings and taunts emerge by It, before they are informed of Stan’s suicide. Richie and Eddie decide to leave while Mike reveals that he met with a Native American tribe who showed him the Ritual of Chüd, a way of destroying It once and for all. Bill and Mike convince Richie and Eddie to stay and finish what was started. A flashback shows Henry Bowers escaping the sewers but getting arrested for the murder of his father. In the present, Bowers is in a mental hospital and escapes with It’s help.
For the ritual to work, each Loser must have an artifact from their past to place in a piece of ancient pottery. Beverly goes to her old home and finds the love letter Ben wrote for her, though she still believes Bill wrote it. Bill goes to the storm drain where Georgie was killed and recovers his paper boat before meeting a boy named Dean, who tells Bill that he lives in Bill’s old house and often hears voices. Ben goes to the town’s high school and finds his old yearbook page, which Beverly was the only person to sign. Eddie goes to a pharmacy and recovers an inhaler. Richie goes to an abandoned arcade where he finds a game token. After escaping individual encounters with It, the Losers use a shower cap from their childhood clubhouse for Stan and Mike finds a rock that started their fight against the Bowers gang. Bill realizes that Pennywise is going after Dean but is unable to save him from being devoured. Traumatized by his failure to save both Georgie and Dean, he returns to the Neibolt house to murder It. The rest of the Losers, after killing Bowers, arrive to help.
The ritual appears to be a success, but a giant version of Pennywise pressures Mike into revealing to the Losers that he never told them they all must die to complete the ritual. The Losers are then thrust into nightmarish scenarios. Eddie saves Richie when he is caught by Pennywise’s deadlights, but is impaled by Pennywise. The Losers regroup and realize Pennywise can be killed if they make him feel smaller than he really is; they insult him and make him physically grow smaller and weaker until they are able to tear out his heart and crush it, ultimately killing It. Eddie dies from his injuries despite Richie’s attempts to save him; the remaining Losers return to the quarry where they once swam together. Beverly, who has realised it was Ben who wrote the letter, shares a kiss with him, and the two start a romantic relationship. Richie returns to the bridge where he had once carved his initials and those of another person, now revealed to be Eddie. He re-carves them before leaving. Mike decides to move out of Derry for a new life. He tells Bill about a letter that Stan wrote to the Losers before his death, explaining that he believed he would’ve held them back, but knew they could defeat It.
The film opens in 1989. Shortly after defeating the evil entity known as Pennywise (Bill Skarsgard), the Losers Club – Bill Denbrough (Jaeden Martell), Ben Hanscom (Jeremy Ray Taylor), Beverly Marsh (Sophia Lillis), Richie Tozier (Finn Wolfhard), Eddie Kaspbrak (Jack Dylan Grazer), Stanley Uris (Wyatt Olef), and Mike Hanlon (Chosen Jacobs) – gather as Bev tells the boys about the vision she saw of all of them as adults when she faced Pennywise. The Losers make a blood pact to return to Derry in the event that they must face IT once more.
27 years later in 2016, a couple – Adrian Mellon (Xavier Dolan) and Don Hagarty (Taylor Frey) – are enjoying a night out at the carnival when they are harassed by homophobic thugs. Even as they walk away from the carnival, the thugs follow them and start to viciously assault them. They throw Adrian over the bridge and flee into the night. Adrian almost drowns until he is pulled out of the water…except the one who pulled him out was Pennywise. Don watches in horror as the monster clown grabs Adrian and takes a huge bite out of his chest. Mike (now played by Isiah Mustafa) overhears a report of the incident over a police scanner, and when he arrives at the scene, he discovers the message “COME HOME” written in blood on the side of the bridge. Mike knows that IT has returned.
We catch up with the other Losers in adulthood. Bill (now played by James McAvoy) is married to Audra (Jess Weixler) and has found success as an author/screenwriter, but he is frequently told that his endings are not good. Eddie (now played by James Ransone) is a risk assessor who is married to a woman, Myra (Mollie Atkinson), who is just as controlling as his own mother. Ben (now played by Jay Ryan) has slimmed down and is a successful architect, though he lives alone. Richie (now played by Bill Hader) is a stand-up comedian. Stanley (now played by Andy Bean) is a partner in an accounting firm. Bev (now played by Jessica Chastain) is a fashion designer, married to the abusive Tom Rogan (Will Beinbrink). Mike calls everyone, and they do not immediately recognize his voice until he mentions he is from Derry. Everybody becomes slightly unnerved by the phone call, and Mike beckons them to return to Derry. Bev tells Tom that she will be returning to Derry to visit friends, but he is paranoid and thinks she is lying to him and is cheating on him since he heard Mike’s name. Tom starts to hit Bev until she fights back and runs away from their home. The other guys start to make their way back to Derry. The only one who doesn’t go is Stanley, as he commits suicide by slitting his wrists in the tub rather than to face the nightmare from his childhood again.
A flashback shows that psychotic bully Henry Bowers (Nicholas Hamilton) survived being pushed down the well by Mike and had washed out of the sewers. When he returned home, police arrested him after they came across the body of Henry’s father and deduced that he murdered him. Today, Henry (now played by Teach Grant) is in a mental institution and has become even more insane. He is visited Pennywise in the form of a zombified Patrick Hockstetter (Owen Teague), who presents Henry with his old knife.
The Losers meet at the Jade of the Orient restaurant and catch up after a long absence. They joke and reminisce, but also note Stanley’s absence. They start to split fortune cookies, only to each get single word fortunes that they realize form a full message. Bev’s fortune reads “Stanley”, and put together, the fortunes read “Guess Stanley Could Not Cut It”. The Losers know that Pennywise has found them. The fortune cookies then start to crack open and reveal hideous little spider-like creatures. The Losers bash at them on the table, which only makes them look crazy when others see them attacking a table. Outside the restaurant, Bev calls Stanley’s wife. Before she can say what happened, Bev knows that Stanley was found in a bathtub, and the other guys figure what happened to him.
Everyone gathers at the hotel where they are staying, and Mike confesses that this is the real reason he summoned everyone back to Derry. They ask Bev how she knew how Stanley died, and she says she has seen how they all die, as she was the only one who saw the Deadlights when Pennywise captured her. Bill goes back to Mike’s house, where Mike drugs Bill’s water to cause him to experience a trippy vision. Mike explains that in all the time he has stayed in Derry, he has studied the history of IT and learned from a Native American tribe of the Ritual of Chud, which can be performed to destroy IT once and for all. He produces a ritualistic piece of pottery with a depiction of the ritual. They bring it back to the other Losers, and Mike explains that they need to gather artifacts from their childhood and place it in the pottery so that they can destroy Pennywise.
Somewhere else in Derry, we see a little girl named Victoria (Ryan Kiera Armstrong) at a football game with her mom. Victoria is lured away by a firefly, and she follows it under the bleachers until she meets Pennywise. He uses the same manipulative trick on her to make her think he is playful, and he appeals to her sympathy when he cries about not having friends, as Victoria is made fun of for a birthmark on her cheek. Pennywise promises to make it go away, only to end up devouring Victoria.
The Losers go to an old clubhouse that Ben built for them over the summer they all became friends. There, they find an artifact for Stanley, which is a shower cap. A flashback shows them as kids with Stanley asking if they will all remain friends as adults. His friends assured him that they would be.
The gang splits up as they head back to their homes in Derry. Bev goes to her old home and meets the elderly Mrs. Kersh (Joan Gregson). She invites Bev inside for tea and cookies as Bev looks around. She finds an old pack of cigarettes, as well as the poem that Ben wrote for her, although she still thinks it was written by Bill. As Bev sits with Mrs. Kersh, the old woman displays unusual behavior. Bev notices what looks like rotted flesh on Mrs. Kersh’s chest. She mentions to Bev that her father joined the circus. Bev sees what looks like a human Pennywise in an old picture. Mrs. Kersh then asks Bev if she is “daddy’s little girl,” as her father had called her. The old woman is then revealed to be Pennywise as she takes on a grotesque and monstrous form that chases Bev out. Before Bev gets away, she sees Pennywise in his human form as “Bob Gray”, who wears his clown makeup and scratches the red lines on his face to taunt Bev.
Richie goes to an old arcade he went to as a kid where he picks up a token as his artifact. In a flashback, he is seen playing a game with Henry’s cousin, and the bully teases Richie for being a “fairy”. Adult Richie is then found and tormented by Pennywise, who claims to know his “dirty little secret.” He takes on the form of a Paul Bunyan statue and tries to attack Richie, but he gets away in time.
Bill goes to an antique shop and sees that his old bike is on sale. He asks the shop owner (played by none other than Stephen King) if he can buy the bike. The owner knows of Bill’s work, but agrees that his endings suck. Bill gets the bike and rides around his old street, passing the sewer where Georgie (Jackson Robert Scott) was taken. Pennywise taunts Bill with an apparition of Georgie calling to him from the sewers. Bill is almost lured in by the monster clown. As he rides away, he sees a kid named Dean (Luke Roessler), whom the gang had seen at the restaurant because he is a fan of Richie’s stand-up. Dean has also seen Pennywise lately after Bill had mentioned it. He firmly orders Dean to get himself and his family out of Derry as soon as possible.
Ben gets an old yearbook page, in which Bev was the only one to write for him. He is haunted by a flashback to his childhood where Pennywise took on Bev’s form to ridicule Ben for his weight, as Pennywise knew that Ben loved Bev, and he still harbors feelings for her to this day. Her form’s head took fire as Ben hid in a locker, only for Pennywise to be in there with him.
Eddie goes to the pharmacy where he would pick up his medications. Creepy Mr. Keene (Joe Bostick) and Gretta (Juno Rinaldi) still work there. Eddie gets an inhaler before he is haunted by Pennywise in the form of his mother being attacked by the Leper (Javier Botet).
Henry kills a guard and escapes the institution. He finds the Losers and attacks Eddie by stabbing him in the cheek. He manages to pull the knife out and stab Henry in the chest, albeit non-fatally, and he runs to his friends for help. However, Henry gets away again before he is caught.
In another Pennywise haunting, Bill sees the message “The fun is just beginning” written, which is what Dean said to Richie at the restaurant, itself a line from Richie’s stand-up. Bill knows that Pennywise is referring to Dean, and he goes to a carnival to try and save the boy after learning he will be there. Bill follows Dean into a hall of mirrors, but Dean just thinks Bill is a crazy weirdo. The two are then found by Pennywise, who bares his long tongue and razor-sharp teeth. Bill desperately tries to kick the glass out to save Dean, but Pennywise breaks through first and brutally kills the boy by chomping into his head hard enough to make it burst. Bill can only watch in horror as he fails to save the boy.
Mike is in the library where Henry finds him and attacks him. Not long after, Richie comes and kills Henry by stabbing him in the back of the head. This causes Richie to puke.
Bill reunites with his friends and vows to kill IT himself. His friends gather their artifacts and they join him at the Neibolt House to face off the evil entity for the last time. While there, they make it into Pennywise’s lair and use the pottery to begin the ritual. The Losers throw in their artifacts, being Bev’s poem, Ben’s yearbook page, Richie’s token, Eddie’s inhaler, the boat that Bill helped make with Georgie, and a rock that Mike recovered from their rock war with the Bowers gang. The Deadlights appear and sink into the pottery with the artifacts, but just when it seems that things worked, out rises a red balloon that produces Pennywise. He faces the Losers again in his true form, as a monstrous spider that still carries his clown face, and he states how he has waited so long to see them again. Mike then reveals that the ritual never worked, and the tribe that attempted it on Pennywise got killed themselves. He splits the Losers up with more nightmare visions, including one of Stanley’s severed head as a spider.
Eddie and Richie find themselves in a similar scenario to when they were kids as Pennywise places three doors with “Scary”, “Very Scary”, and “Not Scary At All” for them to walk through. They see the severed half of Betty Ripsom’s body, as well as a small Pomeranian that morphs into a monster. Meanwhile, Ben and Bev are trapped and split from each other, and Pennywise tries to kill Ben by having him sink into the earth while Bev is trapped in an illusion of a bathroom stall where he is harassed by the forms of Mr. Keene, Gretta, Henry, and her own father. Bev fights back against the visions and manages to pull Ben out from sinking, and she realizes he is the one who wrote her the poem as he had recited it as he was almost dying.
Bill is trapped in what looks like his childhood basement. He sees his young self talking to Georgie, as the image of the little boy blames Bill for lying on the day that he died, as Bill had pretended to be sick so he wouldn’t go out to play with Georgie in the rain. This had haunted Bill for years, and Pennywise knew he blamed himself for it. Young Bill goes to his adult self with a nail gun, but Adult Bill forgives himself and shoots the apparition instead.
The Losers get close enough to fight Pennywise, with Eddie managing to muster up the courage to strike Pennywise himself. As he runs to Richie, however, Pennywise impales Eddie with one of his talons. The Losers try to seek a way out of there, and they figure that since Pennywise is a spider, he can make himself small to try and go after them. They then quickly realize that the only way to make him small enough to defeat him is to force him to believe he is small. They begin to yell at Pennywise and call out all of his otherwise harmless forms before he starts to shrink and shrivel into a powerless shell of his former self. This allows the Losers to pull his heart out of his chest and crush it, destroying him for good. The lair begins to crumble and collapse around them. Richie tries to get Eddie out, but he is already dead. The Losers escape the house and watch as it collapses on itself.
The remaining five head to the quarry where they all swam as children. They think about Eddie and how he would have hated it since it’s so dirty. Richie then starts to cry for his fallen friend, and the others console him. As they continue to swim, Ben and Bev share a kiss. As they later walk home, they see their reflections on a window and see their childhood selves, including Eddie and Stanley. One last flashback shows the group as kids riding their bikes home.
Later on, Bill has gone back to work with writing, and he feels his endings are getting better. He speaks on the phone to Mike, who is thinking about finally seeing the rest of the world. They tell one another that they love each other, and Mike mentions a letter that all the Losers have been getting. Bill finds his letter and sees that it’s from Stanley, written before his suicide. We hear his voice reading the letter over a small montage of the other Losers in the present. Ben and Bev are now in a relationship, while Richie goes to a bridge where he carved his and Eddie’s initials, revealing that he was in love with him. Stanley’s letter states that he knew he could never be brave enough to face Pennywise again, so he removed himself from the equation to give his friends a chance to honor him, which would give them the strength to fight IT. He turned out to be right.
The film concludes with Mike driving away and finally leaving Derry.