Allow me to explain. Nowadays nobody is surprised that King can knock back three novels a year when he has stories to tell. However, as the Bachman books showed, even he was constrained by contracts and other artificial (paper?) barriers. Starting with Danse Macabre, King began to show he didn't need to hide behind a pseudonym any longer to release additional books beyond the "one per year" standard of most writers. I think part of it was due to the freedom of being released from his original publisher. Next thing you know, alongside the throughline of books like Firestarter, Cujo, and Christine came a new subset. The Bachman books were at this point still secret, but Danse Macabre, the first Dark Tower book, and the yet-to-be reviewed-here Cycle of the Werewolf ran alongside the "regular" books. However, his original publisher apparently wasn't through with him, as he left his contract a book short. He had written something so dark and horrid that he had indefinitely banished it to the darkest recesses of his desk, the unfilled final act of his first contract. So even though Christine was the Novel of the Year for 1983, Pet Sematary comes along for the ride, and likely ends up upstaging its predecessor.
It's quite a testament for this book to be so scary that even Stephen King wanted to keep it squashed, but there's nothing like the phrase "contractual obligation" to get something released against one's will. As King reminded us in Danse Macabre, horror is about the things that scare us. Typically the scarier the premise, the better the book at succeeding in the genre. 'Salem's Lot works because vampire are scary. Cujo works because rabid dogs are scary. The Stand works because global pandemics (as in the ones that kill 98% of humanity, not 0.5%) are scary. Of course vampires aren't real, rabid dog attacks are rare, and pandemics are a shared societal problem. What is really scary? Something that invariably happens to all of us: the loss of a loved one. Scarier even is the notion that their death was our fault. Fundamentally the death of a child, as a cruel reversal of the natural order, tears at all of us, even those without children of their own. It is one of the darkest places we can go, and Stephen King went there.
Pet Sematary has two distinct parts: the before and the after. Part one is plenty sad. A family wants to make a new start, but the choice of house is challenging. It borders the back-of-beyond Maine, it's by a road that "uses up animals", and there's some pet sematary (sic) a short walk away. It's like they walked into the jaws of death. The father, Louis Creed enjoys perhaps the single worst first day any doctor has ever experienced, with a student dying on the operating table after a gruesome accident. That student takes Louis on a beyond the grave tour of a place beyond the pet sematary that must be avoided at all costs. His beer-loving neighbor Jud, not aware of this, lets Louis in on a little secret after the family cat dies, that death is not the end and the secret just happens to be the very place Louis's spirit-guide told him not to go. Aw, heck, it's just a cat though, so Louis goes there (in multiple senses) and revives Church the Cat. It's all sorts of wrong though. Church smells awful, has a mean disposition, and, when Jud's wife succumbs to her terminal illness, Jud does NOT take her there. Nevertheless, Louis manages to wrap up the book's first part with a perfect day of kite-flying with his son Gage and in spite of the deaths and questionable resurrections all seems to have turned out fine.
It turns out the kite-flying was just one last deep breath before Stephen King takes us down to plumb the watery depths of the book. It had been teased throughout the first part, but the unthinkable strikes when Gage is run down by a truck. Even though fully aware of how messed up Church turned out, and with Jud strongly discouraging him from taking another trip beyond the deadfall, Louis's heart overrides his brain and he works his long game to bring back Gage. He packs off his wife Rachel and daughter back to Chicago with the in-laws, spends about 100 pages fighting his way into the cemetery (the people one) and moving his son's corpse to the new burial ground to resurrect him. If you thought Church was a bad resurrection experience, Gage is something else altogether. Jud knew from past experience that people come back evil, but Louis, rent by grief, doesn't care about any of that. Reminiscent of that awful experience of Jud's, Gage returns as a full-on murder baby, killing Jud and his own mother, who rushed back from Chicago at just the wrong time. Even with all the bloodshed and destruction (Louis kills Gage and Church....again), Louis is spotted taking his Rachel toward the pet sematary, so we can relive the nightmare over and over.
Being Stephen King, there's a lot of supernatural stuff to unpack, as usual. The whole notion of resurrecting the dead is undoubtedly not something natural, there is some mystical Native American demon figure that seems to be pulling on the strings. This creature has its hooks in everyone's lives, taking the form of Rachel's bogey(wo)man, his sister Zelda. So it would seem that the secret burial ground isn't ginning up the inherent evil in Church, Gage, and all the rest (I mean, how much evil could Gage have took on at that age?!), but infecting them all with this omnipresent demon. Said demon may also be behind Louis's weird dream visions, as well as his daughter's inexplicable way of knowing something was wrong from over 1000 miles away....and inadvertently sending Rachel to her death. So, we can say perhaps there's a demon dwelling in all of hearts, preying on our weaknesses, exploiting the guilt, and that it isn't just us alone driving these grim decisions. On the flip side of the supernatural, this is one of King's most autobiographical novels, as the introductory essay explains, with many elements of the story being lifted from his own experiences (including the pet "sematary" iteself), revealing his own vulnerabilities about this own young family.
So while the next "proper" novel may be It, there is still much to explore before we get there. One more Bachman book, an oddball werewolf novella, a monster sized collaboration with Peter Straub, and the second great short story collection must all be addressed first. Pennywise will need to wait just a little bit longer.