It’s back. The second half of Stephen King’s horror bestseller about the terrifying clown (is there any other kind?) has now been adapted as a separate but frankly laborious film to follow the first one. That was the story of how a bunch of middle-school kids in a small American town in the 1980s banded together to defeat a homicidal harlequin of hell called Pennywise. His relationship to them made him an antichrist version of ET. Now, almost 30 years later, they are all grown up and must return to their home town to face the horrible Pennywise all over again – as adults. Screenwriter Guy Dauberman (who worked on The Conjuring franchise) adapts the second half of King’s novel and the director once again is Andy Muschietti.

There is some lively stuff here, including a few sensational cameos and interesting ideas about confronting one’s personal demons, about homophobia, abuse and depression. It is also about the ubiquitous availability of the past in the digital age and the permanent reunion-stalkerthon of social media, and about the way guilt and shame are built into what we choose to remember and forget about our teenage years. But, like the first film, it becomes a virtual non-narrative anthology of standard jump-scares that could be reshuffled and shown in any order. The second time around, your tolerance for this is tested to destruction and beyond because, unlike the first movie, it is just so pointlessly long: approaching three hours, with our heroes finally beginning to assume a glassy-eyed solemnity like Hogwarts graduates or the Fellowship of the Ring. Muschietti is even hinting at a possible third chapter.

The way they battle Pennywise as grownups is not much different from the way they did it as kids (although, arguably, these new confrontations are unlocking painful childhood memories) and Chapter Two seems to consist of an indefinite number of big, scary set pieces, featuring interchangeable snaggle-toothed creatures, or occasionally gigantic, fairground-sized monsters lurching grotesquely up out of nowhere. The scenes deliver reasonably efficient scares, but with the tension level repeatedly and disconcertingly reset afterwards to zero: the scenes don’t develop or accumulate anything within a story arc and it feels as if the movie is jumping the shark and jumping back again, increasingly spending more and more time the wrong side of the shark and finally staying there.

The situation is that Pennywise (played again by Bill Skarsgård) mysteriously returns to the little town of Derry, Maine, metaphysically reconfigured or reincarnated, perhaps, by an ugly display of homophobic abuse – an interesting acting cameo here for the Canadian director Xavier Dolan. Mike (played now by Isaiah Mustafa) is the only one of the gang to have stayed behind in Derry, and he gets in touch with everyone. Smart, flame-haired Bev is now a well-off professional played by Jessica Chastain, with troubles in her private life that chillingly mirror what she endured as a child; nerdy bespectacled Richie (Bill Hader) is a wisecracking standup comic; Ben (Jay Ryan) has lost all his plumpness and is a wealthy architect and serious hottie – to the astonishment of those who knew him way back when. The sensitive Stanley (Andy Bean) is a troubled, complex adult, and Bill, the boy whose kid brother was fatefully abducted by Pennywise at the story’s beginning, is now a bestselling author whose work is lucratively adapted for the cinema – remind you of anyone? – and he is played by James McAvoy: a writer wrestling with the problem of endings, something troublesome in art as in life.

Facebook Twitter Pinterest The gang’s all here … It Chapter Two. Photograph: Allstar/New Line Cinema

Interestingly, they have all suppressed the supernatural horror they experienced. It was the only way to get on with normal adult life, and the movie amusingly shows how Mike’s news about Pennywise’s reappearance triggers a convulsive spasm of irrational anxiety in each case: the return of the repressed.

But disappointingly, It Chapter Two finds no clear and satisfying way of engaging with the obvious question: is Pennywise a metaphorical expression of the gang’s inner horrors, or a standalone devil whose existence has nothing to do with the psychology of those ranged against him, or something between the two? Pennywise can be read in any or all of these ways, but there is nothing very interesting or revelatory about the clown’s figurative possibilities because they are not teased out within the story.

The grown-up gang of heroes may or may not be taming their private demons in tandem with Pennywise, and tackling your private agonies is a lifelong process. But the thought of these people lumbering back as oldsters in Chapter Three to do the same old scary-movie things with Pennywise all over again fills my heart with the kind of dread that nothing here approached.

• It Chapter Two is released in Australia on 5 September and in the UK and US on 6 September.