“看到X”是“看到1.5” chronologically, taking place between the first and second films in this granddaddy of torture porn franchises. Quality-wise, though, it is closer to a 10 than a zero, which cannot be said about most of the other nine movies in this distressingly popular series.

The squeamish won’t enjoy it. You’ll like it better if you’re not too keen on the Eighth Amendment’s prohibition against cruel and unusual punishment. Best way to watch it is without a moral compass.

Yet this first totally linear narrative in the “Saw” saga is a well-told tale, with some solid characterizations and quite decent twists. Except for an early fake-out or two, Josh Stolberg and Peter Goldfinger’s script is rather slow getting to the, ahem, good stuff. But once it does, the slice-o-matic contraptions and self-mutilating predicaments that protagonist Jigsaw devises show some diabolical genius.

Sorry, did we call him Jigsaw? In “Saw X” Tobin Bell, the actor who portrays both that master trap maker and his alter ego, retired civil engineer John Kramer, definitely emphasizes the latter. To him, the folks his traps torment aren’t victims but lost souls he wants to teach to appreciate life and smell the roses. That is, if they come out of his frightening games with their noses intact — or their heads still attached.

In this installment, set between 2004’s “Saw” and 2005’s “Saw II,” John heads to Mexico to get an experimental treatment for the brain tumor that’s killing him. It shouldn’t be brain surgery to figure out that it’s a scam, but Bell sells John’s quiet desperation to believe. The sadistic, self-styled savior of those he judges even sheds a tear here and fixes a kid’s bike; we could almost mistake John for a hero.

Bell has never acted so much in a “Saw” movie before, and in a wispy, whispery way clearly relishes this star turn opportunity. The octogenarian, though fit, looks his age, rather than like the stricken mid-50s John Kramer he’s portraying. But if you go to one of these movies expecting total believability, I’ve got a cure for cancer to sell you.

Shawnee Smith is back as well, and a hoot as Jigsaw’s not quite demented enough apprentice Amanda, who is learning the ropes — made from human intestines — so to speak. Norwegian actress Synnøve Macody Lund (“Headhunters”) is delectably amoral as Cecilia Pederson, the quack who doesn’t care about her co-conspirators any more than she does her dying clients.

Cecilia’s henchpeople are played by a fine Latino ensemble: Joshua Okamoto, Renata Vaca, Octavio Hinojosa and Paulette Hernandez. Pederson’s exploitation of Mexican labor is implicit to the piece but never mentioned, perhaps because the movie does the same thing, reducing the locals to meat for Jigsaw’s grinders. Still, each actor registers more than fear and pain.

The infernal devices do offer their captives quite cinematic ways to die. In keeping with the movie’s theme, most have a medical component, and the coolest ones exhibit some Aztec flair — though director Kevin Greutert didn’t do all he could have with the film’s Mexico locations. In the end, “Saw X” looks like every other postindustrial torture chamber in the franchise.

Still, Greutert, who’s edited all 10 of these movies and now directed three, has an instinct for what works best and what it can mean. Though he’s driven by mortality and moral superiority, John has a moment here when he reckons with his twisted rationale. His body may still have a few months to live, but his jigsawed soul dies right there.

Bob Strauss is a freelance writer.