B-

James Wan and Leigh Whannell haven’t had a great deal of luck since they struck it rich with “Saw”—except financially, of course, since they’ve gotten a cut from all its wretched sequels. Their last attempt to create a horror franchise (“Deep Silence”) was a disaster, and the revenge melodrama “Death Sentence” was even worse. But with “Insidious” they manage a comeback of sorts—if you consider two-thirds of a good, cheeky thriller enough to call a comeback.

At heart Whannell’s script is just the latest in a long line of haunted house pictures, and it owes a good deal to “Poltergeist” and “Paranormal Activity”—in fact, the director of the latter is one of the producers here. But for the first hour or so it’s very cannily assembled, as it follows the Lambert family’s move into a spooky new house. Dad Josh (Patrick Wilson) is a high school teacher, while stay-at-home mom Renai (Rose Byrne) is an aspiring songwriter. They have three kids, two young boys and a baby girl, and seem a happy brood.

All that changes when little Dylan (Ty Simpkins) falls off a ladder while investigating the attic and bumps his head. The next morning, he won’t wake up, and the doctor informs his parents that he’s fallen into an inexplicable coma. Eventually the child is brought home, and while he continues in his comatose state, the house begins to be troubled with what seems to be poltergeist activity—loud noises, creaking doors, and finally strange and unsettling apparitions. These become so unnerving that Josh begins spending his evenings at school, leaving Renai to bear the brunt of the terrors.

At Renai’s insistence the family moves to another house, but the mysterious apparitions follow them there. Who should now intervene but Josh’s mother Lorraine (Barbara Hershey)? She introduces her son and daughter-in-law to a medium, Elise (Lin Shaye), who sends two true-believer ghostbusters (Angus Sampson and Whannell) to check out the house with their homemade equipment before arriving on the scene herself, ready to look into matters directly.

So far, so good. Up to this point “Insidious” is a very effective blend of scare tropes (slamming doors, spectral faces in the shadows, strange figures bounding down hallways), tinged with a wry sense of humor that tells you tongue is firmly in cheek. Though one hopes that the awful music Renai is shown composing is intended as a joke, the latter element is especially pronounced when Elise and her minions show up; Shaye plays the woman as though she were a latter-day Madame Arcati (the gas-mask getup she uses when trying to communicate with Dylan is sure to elicit a laugh), while Sampson and Whannell do an amusing routine as goofy partners who constantly bicker over which of them is the more important. Hershey’s turn as the concerned mother-in-law has a rich vein of the absurd in it, too.

Unfortunately, it’s about at this point that the movie goes into explanatory mode, with increased visual effects but diminishing returns in the delivery of both shocks and chuckles. Elise offers a diagnosis of astral projection that has sent Dylan off into the realm of deceased and demons that she terms “the Further,” and Josh—who, it turns out, has the same ability to leave his body as his son—has to go there to find the boy’s lost spirit and return it to his body before it’s taken over by one of its dark denizens. That leads to a long sequence that comes across like a trip through an amusement park haunted house, which—though elaborately mounted, as the finale of “Dead Silence” was—isn’t particularly frightening or amusing. One gets the feeling the makers merely wanted to show off their ability to fashion oddball compositions and weird figures for their own pleasure rather than ours. And the addition of a couple of morbid twists at the close doesn’t save the day.

Still, until the misguided last act, “Insidious” manages to generate some genuine chills and a few chuckles. It boasts a classy production design by Aaron Sims and expert art direction by Jennifer Spence, as well as glossy widescreen cinematography by David Brewer and an effective background score by Joseph Bishara. And the performances are generally fine; if Wilson, as usual, is a rather pallid presence; Byrne adds some heft to the proceedings. And Hershey, Shaye, Sampson and Whannell certainly do their part.

Unlike the best horror films, though, it probably won’t stick with you long after the lights come up.