"It" by Stephen King is about a group of seven kids in Derry, Maine, who face down a shape-shifting evil force that preys on their worst fears over a 30-year period from the 1950s to the 1980s. It presents itself as a sadistic wisecracking dancing clown named Pennywise. The story takes place in two segments: one when the group is young and the other when the group returns to the town as adults.
In the first segment, the group of kids, labeled The Loser's Club by the town bullies and led by a boy named Bill, experience terror at the hands of Pennywise when the monster lures Bill's little brother Georgie into the sewer and to his death. The event traumatizes Bill and leaves him with a stutter. Pennywise tortures the group of children in their dreams, leading them to mount an expedition into the sewer to kill It. The town bullies follow them, and Pennywise kills the bullies. The Loser's Club escapes, vowing never to return.
When a 6-year-old girl goes missing in Derry 30 years later, one of the group calls the other members back to town. When the gang regroups, the tortured dreams begin again, and the only way to get them to stop is to venture back to the creature's lair and finish it once and for all.