In October 1988, stuttering teenager Bill Denbrough gives his seven-year-old brother, Georgie, a paper sailboat. Georgie sails the boat along the rainy streets of small town Derry and is disappointed when it falls down a storm drain. As he attempts to retrieve it, Georgie sees a clown in the sewer who introduces himself as “Pennywise the Dancing Clown”. The clown entices Georgie to come closer by talking about the circus, then severs his arm and drags him into the sewer drain.
The following summer, Bill and his friends (loudmouth Richie Tozier, hypochondriac Eddie Kaspbrak, and timid Stan Uris) run afoul of bully Henry Bowers and his gang. Bill, still haunted by Georgie’s disappearance and the resulting neglect from his grief-stricken parents, discovers that his brother’s body may have washed up in a marshy wasteland called the Barrens. He recruits his friends to check it out, believing his brother may still be alive.
“New kid” Ben Hanscom learns that the town has been plagued by unexplained tragedies and child disappearances for centuries, and is lured into the basement of the library by Pennywise, before escaping the library. He is attacked by Bowers’ gang for being fat and has an ‘H’ carved into his stomach. He is able to escape before Henry can finish his name and flees into the Barrens and meets Bill’s group. They find the sneaker of a missing girl named Betty Ripsom, while a member of the pursuing Bowers Gang, Patrick Hockstetter, is killed by Pennywise looking for Ben. The Losers see Ben bloody, and rush to the nearest drug store to fix him up. They don’t have enough money, however, and Beverly Marsh, a classmate and friend of Ben bullied by mean girls over rumors of promiscuity, helps them in stealing the products.
Beverly helps clean Ben’s wound and joins the group; both Bill and Ben develop feelings for her. Later, the group befriends homeschooled black kid Mike Hanlon after defending him from Bowers in a rock war. All the while each member of the group has encountered terrifying phenomena in various forms; these include a menacing clown for Richie, a headless boy for Ben, a fountain of blood for Beverly, a diseased and rotting man known as a Leper for Eddie, a creepy painting come to life for Stan, Mike’s parents burning alive, and finally a phantom Georgie for Bill.