What is the summary of the book "It" by Stephen King?

It by Stephen King is a novel about friendship and the magic of childhood. The novel centers around seven core characters, friends who bonded as children during a summer of darkness. Twenty-seven years later, they reunite to fulfill a promise made that terrible summer. Evil lives under their hometown and, for some reason they do not understand, these seven have been destined to bring an end to the terrible cycle of death and destruction. These friends fought It once before, but now It is back, and they must end the evil for good. It is a novel of magic, mystery, and horror that will entertain readers of all ages.