It is the fall of 1957 and it has rained for a full week, causing the streets of Derry, Maine to flood. Ten-year-old Bill Denbrough helps his younger brother, George Denbrough, make a waterproof paper boat so that the six-year-old can go play in the rain. To get paraffin wax for the boat, George must go to the basement, which he hates. George reaches the cellar door, opens it, and stands at the top of the stairs, certain that “It” lurks somewhere down there. He proceeds downstairs and finds the can of wax. George stares for a while at the picture of the turtle on the lid, wondering where he has seen it before. When Bill calls after him, George awakens from his daydream and brings up the materials. George watches admiringly as his brother waterproofs the boat. In gratitude, George kisses him before going out. This is the last time Bill sees his younger brother.
George chases after his boat as it rushes through the floodwaters in the street. The boat floats toward a storm drain and gets caught. When George peers down into the drain, he sees a pair of yellow eyes staring back at him. The eyes then turn blue, like those of George’s mother. The eyes belong to a clown who introduces himself as “Mr. Bob Gray, also known as Pennywise the Dancing Clown.” The clown tells George that the storm swept him and his circus into the sewer. George leans closer and smells delectable scents mixed with manure and the smell of dead things. The clown offers George his boat and a floating balloon. As George reaches forward, the clown’s eyes change, and Pennywise pulls the boy into the darkness, ripping George’s arm out of its socket. The boy dies instantly. Dave Gardener, a neighbor, races out of his house and carries George’s body back to the Denbrough house.
It is now 1984. Adrian Mellon, a gay man, is beaten to death and thrown off of the town’s Kissing Bridge into the Canal. The youths who assault Mellon and his partner, Don Hagerty, include Christopher Unwin, Steve Dubay, and their ringleader, John “Webby” Garton. Chris Unwin reports seeing a clown drag Mellon under the Kissing Bridge. Hagerty says that there were thousands of multi-colored balloons under the same bridge. News of the murder and the report of a strange clown prompts local head librarian Mike Hanlon to place six calls to six old friends.
The first call is to the home of Stanley Uris in suburban Atlanta. On the evening of May 28, 1985, Stanley and his wife, Patricia Uris, are watching television. The call prompts Stanley to take an evening bath, which his wife finds strange. When Patricia goes to check on him, she finds the door locked. When she gets the door open, she finds Stanley dead in the bathtub, the water red from his blood. On the wall tile, he has scrawled a message in his blood: “IT.”
The next call is to Richard Tozier, now a Los Angeles radio personality. While Richie makes arrangements with his travel agent, Carol Feeny, the renowned architect Ben Hanscom receives the next call. Hanscom lives in Nebraska. After getting his call, Ben takes what he suspects may be his last drink at the Red Wheel, a bar that he frequents. Eddie Kaspbrak’s telephone rings around this time. Eddie, the owner of a chauffeuring company, asks his wife Myra to substitute for him in picking up and driving Al Pacino around Manhattan. Myra, an overprotective woman who is similar to Eddie’s mother Sonia begs Eddie not to leave, but he goes anyway. Meanwhile, in Chicago, the dress designer Beverly Marsh Rogan receives a late-night call. She tells her husband, Tom Rogan, that she must leave. Tom forbids her to go and a fight ensues. This time, Beverly refuses to obey her physically abusive husband, whose habits resemble those of her father, and beats him with the belt that he normally uses on her. She becomes so anxious to leave the house that she leaves her wallet behind. With the help of her friend Kay McCall, she is able to get the money that she needs to get back to Derry. The final call goes to the writer Bill Denbrough, who is in England, where he and his wife, the actress Audra Phillips, are working on Attic Room, a film adaptation of one of his novels.
Mike Hanlon is the only one who has remained behind in Derry—a town of 35,000. He collects local folklore and serves as the town’s “watchman,” on the lookout for It. He and his six friends—nicknamed the Losers’ Club—sent It away in 1958. Twenty-seven years later, he tells them that it is time to finish the job they started. They must destroy It and end its reign of terror over Derry.
Every member of the Losers’ Club has a characteristic that makes it difficult for them to fit in. Ben is overweight and overfed, due to fears of poverty harbored by his single mother, Arlene Hanscom. Bill stutters and is as shut off from his parents as he is from his peers. Eddie is the son of an overprotective hypochondriac of a mother who has convinced him that he has asthma. Beverly comes from a poor and abusive home. Richie comes from a comfortable household but unintentionally irritates nearly everyone with his barbed sense of humor. Mike and Stanley come from more secure and loving homes, but they are socially outcast due to being black and Jewish, respectively. Another link that binds the group is that, after the death of George Denbrough, none of them has any siblings, resulting in their ability to find fraternity with each other.
The main tie that binds, however, is that each has a story to tell about It. Richie was the last to experience It, in the form of a werewolf, reminiscent of the monster from I Was a Teenage Werewolf, a film he sees at the Aladdin Theater. He and Bill flee from the monster on Silver, Bill’s bike. In their childhood, the Losers’ Club is able to elude death at the hands of It, but a myriad of other children are found dead or turn up missing. One of these, Edward Corcoran, remains missing until his mother declares him legally dead in the 1960s. Edward, like Beverly, also comes from an abusive household. His stepfather, Richard Macklin, regularly beats him and his brother Dorsey, resulting in the bludgeoning death of the latter. The Losers’ Club knows that Richard is not responsible for Edward’s death, which they sense when it occurs. Edward is attacked and killed by a creature that is half-fish and half-amphibian. Mike Hanlon finds Edward’s pocketknife and spots of blood beside the bench that Edward tripped over on the night of his murder, trying to escape.
It, the children learn, can shapeshift. The group also finds out that It is what the Himalayans call a taelus, or “skin-changer.” Mike has seen It take the form of a giant bird, similar in appearance to a bird that pecked at him once in his infancy. Eddie sees It transform into a leprous hobo at the house on 29 Neibolt Street. When Bill looks through George’s old photo album, It causes the eyes to move in a photo of George. Henry Bowers, the violent bully who breaks Eddie Kaspbrak’s arm and carves a letter “H”—the beginning of “Henry” into Ben Hanscom’s stomach—sees a Frankenstein-monster rip the heads off of his friends and fellow bullies, Victor Criss and Reginald “Belch” Huggins. Meanwhile, Beverly hears voices from the kitchen and bathroom sink drains. In one instance, a gush of blood springs out of the pipes and covers the walls. Her father, Al Marsh, cannot see the blood; only she and her friends can. Later, she sees Patrick Hocksetter get attacked and killed by mutant leeches.
It, the children learn, is not only a terror within their time but a presence that has existed throughout Derry’s history. It is present during Derry’s transformation from “a sleepy little shipbuilding town into a booming honky-tonk.” It is present in 1929 during the town’s ambush of the Bradley Gang and participates in the shootout. It is also present during the burning of the Black Spot in 1930. The Black Spot is a speakeasy formed by Mike’s father, Will Hanlon, Dick Halloran, and some other black soldiers stationed in Derry, which gets burned down by white supremacists.
Bill, Ben, and Richie decide in 1958 that they have to send It away by making a silver bullet. They learn this from the movies. With a silver slug, a slingshot, and her excellent marksmanship, Beverly sends It down a drainpipe. They learn, however, that this only repels It. The key to sending It away for good is by performing the Ritual of Chüd, in which the attacker bites down on his or her tongue, prompting It to bite its own. The attacker then tells jokes. If the attacker laughs first, It earns the right to kill. If It laughs first, It must go away. Through a combination of this ritual, as well Beverly’s insistence that the boys make love to her to solidify the strength of their circle, the Losers’ Club succeeds in sending It away, but not in killing It.
While members of the Losers’ Club go on to achieve success in adulthood, Henry Bowers is locked away in Juniper Hills, a mental institution for the criminally-insane. He has been here since he murdered his father, Butch Bowers, with a switchblade mailed to him by Bob Gray. Henry is also blamed for the murders of his friends, Victor and “Belch,” and for that of Veronica Grogan, whose underwear is found under Henry’s mattress. One night, It leads him out of the institution and back to Derry. Henry first finds Mike in the public library and the two have a knife fight that leaves Mike nearly dead from a wound to his thigh. Mike notices that Henry has been possessed by It, which uses people as its “dogsbody,” or servant. Henry then goes to Eddie’s room at the Town House hotel. Eddie succeeds in killing Henry with a letter opener.
Both Tom Rogan and Audra Phillips have followed their spouses to Derry and unknowingly stay in hotels located beside each other. That night, they each have a dream. Tom dreams that he is Henry and has killed his father. Audra dreams that she is Beverly. When she awakes, Audra suspects that Bill is with another woman. Indeed, he and Beverly have spent the night together. Eddie calls Bill’s room to tell him that he has killed Henry. The group also finds out about the attack on Mike, who is recuperating in the hospital. When the five are back together, they join hands and rescue Mike from an attempt by Mark Lamonica, a nurse who has been possessed by It, to kill Mike with a deadly shot. Tom, too, has been possessed by It, which uses him to kidnap Audra.
That evening, the five remaining members of the Losers’ Club—Bill, Ben, Richie, Beverly, and Eddie—enter It’s lair, and discover that It has transformed into a giant female spider. Also there in the darkness is the Turtle. The Turtle speaks to Bill and apologizes for having made It, along with the rest of the universe, after vomiting from a bellyache. Richie looks up into It’s web and sees Audra. She has entered a catatonic state and appears almost like a waxwork. Richie does his Irish cop impression to make It laugh, and the performance of the ritual saves Bill, but not Eddie, who gets his arm bitten off by the spider. Eddie later dies. While Ben stomps on It’s eggs, Bill squeezes his hands around It’s heart until the organ bursts. It dies.
It is now morning in Derry, and the town is bizarrely experiencing an earthquake. The underground portion of the Canal’s supports collapses, as does downtown Derry. The glass corridor that connects the adult library to the Children’s Library explodes. The remaining four members of the Losers’ club emerge from underground.
Bill notices that his stutter is disappearing. Mike notices that his memory is fading. Ben and Beverly start a new life together as a couple and drive off to Nebraska. Bill, too, is starting to lose his memory. He forgets what led to Audra’s catatonic state, but he is determined to free her from it. He mounts Silver with Audra behind him and drives away from memory “but not from desire.” He pumps the pedals, moving the bike so fast that Audra awakens, startled. Mike has the final word, and surmises that no one will ever see his diary. He concludes that, even if the group forgets each other during their waking hours, perhaps they will remember everything, particularly their love for each other, in their dreams.