This It article contains spoilers.
Stephen King’s 1986 novel It takes place in two different timestreams: the past (1958) and the present (1985). In both eras, the seven friends known as the Losers’ Club must come together to defeat the ancient supernatural entity that resides deep under the town of Derry, Maine and emerges to terrorize and murder its inhabitants, especially children, usually in the shape of a clown named Pennywise. They seriously wound It in 1958 (the movie switches the earlier period from 1958 to 1988) as children, then come back — to destroy It once and for all 27 years later as adults.
The way the book is written, King weaves the two timelines in and out of each other, cutting more rapidly between the two until they seem to almost merge together — he even does things like stopping in mid-sentence in 1958 and picking up with the end of the sentence in 1985 (or vice versa) to achieve the effect of the past and the present becoming one. That is, in a way, what happens, as the adult members of the Losers’ Club must draw upon their childhood memories — which have been repressed — to find their way back to what they’ve forgotten in order to end It’s reign of terror for good.
We’ll get to how they vanquish the thing in a moment. Since this film version of It was conceived as two movies, It Chapter One focuses only on the Losers’ Club as kids. That’s a big change from the book. It’s a better way to tell the story — there’s no way that even the most gifted screenwriter could fit all the important events of both timelines into one film, even a long one — and it allows the audience to fully empathize and bond with the kids, instead of distractingly and perhaps confusingly between the two time periods.
The ending of the film finds the Losers’ Club baited into entering the sewers of Derry and finding It’s lair in order to rescue their sole female member, Beverly (Sophia Lillis), who has been abducted by Pennywise after she escapes an attempted rape by her own father. The kidnapping itself is a departure from the book, as is Beverly’s glimpse of the “deadlights.” The “deadlights” are It’s true form, which exists outside of time and space and can only be perceived by the human mind as destructive orange lights. They render Beverly catatonic until the Losers find her and secret admirer Ben (Jeremy Ray Taylor) plants a nice kiss on her mouth, the power of his love bringing her back to the living.
That love — the shared affection and loyalty of the seven friends — is ultimately It’s undoing. Bill finally overcomes his grief over Pennywise’s murder of his little brother Georgie by confronting a spectral version of the little boy manifested by It and destroying the façade, revealing Pennywise underneath. Once he has accomplished that, Bill can unite with the others and together they overcome their own fears — each manifested again in turn by Pennywise — and attack the creature both physically and with their imaginations, wounding it badly and sending it back even further down into the depths beyond the sewers and tunnels underneath Derry.
King’s book is all about the end of innocence and the confrontation of childhood fears, as well as the bonds of love, and it is those themes that are reflected most strongly in the ending of the movie as well. Bill finally comes to terms with his own personal quest to alleviate his guilt and grief so that he can join with the others in a united front against Pennywise, while each of the other children also conquer a particular fear or make a stand against whatever is holding them back so that they can do the same. Once they do that, Pennywise is vulnerable, weakened and forced into retreat — but not death.
The defeat of It by the children in the book is handled quite differently. When they confront the thing in its lair, they see it in a very different form than a clown. Since its true form is beyond human comprehension, their minds translate it as a giant spider. Bill confronts It mostly alone and is flung by the entity into another dimension where he is nearly brought head-on into the deadlights, which can drive anyone who looks into them insane. But while outside the bounds of our reality, he also meets the Turtle (again, a mental approximation of a presence beyond human understanding). The Turtle, whose name is Maturin, created our universe but exists like Pennywise/It outside of our reality. While Maturin doesn’t involve itself in puny human matters, it does offer Bill advice on how to stop It.
Surreal stuff, right? And perhaps too out there to attempt to put on film (the 1990 miniseries did feature an animatronic spider which turned out to be an unfortunate choice). But if you think that’s weird, what happens next remains one of the most controversial sequences in all of King’s extensive bibliography. With It defeated, the kids find themselves lost in the sewers and possibly unable to escape. They need to bond together again after the monster’s savage attacks. So 11-year-old Beverly decides that each of the six boys must make love to her right there in the tunnel to form an emotional and physical connection that will remain unbroken. King writes this sequence with as much care, grace, and sensitivity as he can, but it’s still essentially group sex involving six barely pubescent boys and a girl — a scene you can pretty much rest assured will never make it to the screen no matter how many times It is filmed.
The adults’ defeat of the spider is similar but much more final, with both Bill and Richie risking the deadlights to literally tear the thing’s heart out. And since they’re grown men and women now, there’s no lovemaking scene to denote their passage from childhood to adulthood. Director Andy Muschietti has hinted in recent interviews that the second It film will delve more deeply into the more surreal aspects of the Losers’ battle against the entity, although how much if any of the spider, the deadlights, the Turtle, and the Macroverse (the void outside our universe) will be deployed remains to be seen.
As in the book, at the end of the film the seven children make a solemn vow and take a blood oath that if It ever resurfaces in Derry, they will all come back — no matter where they are or what they’re doing — to fight the entity once again. With this first movie looking like a tremendous success — both with critics and at the box office — a sequel now looks like a sure thing. Once again the Losers’ Club will descend under the ground and go into battle, armed only with their love and friendship for each other. In both the book and the movie, that’s more than enough.