One of the more amusing aspects of “Insurgent,” Robert Schwentke’s adaptation of the second volume in Veronica Roth’s YA trilogy, will come when the book’s fans notice how far the script by Brian Duffield, Mark Bomback and Akiva Goldsman departs from its source. A negative reaction would certainly be ironic, given that the tale celebrates divergence. But more importantly, the movie itself won’t provide much cause for jubilation, although the fact that it was made at all—when the box office take for the first installment fell far short of “Hunger Game” standards, and so many other YA trilogies never even made it to sequel stage—has to be considered a signal achievement.

Not that “Insurgent” is terrible—in fact, it’s an improvement on its predecessor, which is somewhat surprising since the reins were turned over to a director whose most recent effort was the utterly dreadful “R.I.P.D.” For one thing, it isn’t as silly as “Divergent,” which had to concentrate on explaining the rules and processes of the nonsensical post-apocalyptic society that was the basis of Roth’s narrative. So instead it can put its emphasis on action pure and simple, though it has to pause all too often to allow heroine Beatrice “Tris” Prior (Shailene Woodley) to bemoan her losses—and the fact that she feels so responsible for them. Simply put, in a genre filled with disasters this is a workmanlike job, if an uninspired one—which is the fault of the source as much as the film itself.

As the movie opens, Tris is still on the run—along with her handsome boyfriend, ex-Dauntless Four (Theo James), her cerebral brother Caleb (Ansel Elgort) and snarky, unreliable Peter (Max Teller)—from Jeanine (Kate Winslet), leader of the Erudite faction who’s established a virtual dictatorship over the now-walled-in remnant of Chicago. The four have taken refuge in an Amity settlement run like a rustic commune by Johanna (Olivia Spencer), but they’re found by Jeanine’s minions, led by evil Eric (Jai Courtney), and though Peter predictably changes sides, as is his wont, the other three escape by jumping a train. There they find a group of rebellious Factionless folk led by Edgar (Jonny Weston). After an initial altercation, he takes them to the Factionless camp, where they find Evelyn (Naomi Watts), the mother Four presumed dead, in charge.

Because of Four’s anger with Evelyn for abandoning him, however, they don’t stay long. Caleb goes off on his own, and Tris and Four proceed to the Candor community headed by Jack Kang (Daniel Dae Kim). There they endure a truth serum test that reveals both Tris’ guilt over the deaths for which she feels responsible and Four’s love of her, but also proves their innocence of Jeanine’s allegation that they were instrumental in a destructive attack on the Abnegation faction. Their relative safety is soon destroyed, however, when Eric and his army of thugs invade Candor seeking a Divergent powerful enough to serve as the conduit through which Jeanine can open an ancient box containing a message from the founders that she believes will put an official imprimatur on her dominion.

Wouldn’t you know it, Tris proves the perfect instrument, and Jeanine uses her customarily ruthless tactics to force the girl to submit to a series of five “sims,” or virtual-reality simulations, that will unlock the box’s secrets, which turn out to be something she didn’t expect. A coda indicates that the final installment of the story, “Allegiant” (which reportedly will be extended to two movies), will place Evelyn in a leading role. The whole box scenario is the invention of the screenwriters, apparently designed, at least in part, to allow for the insertion of a big special-effects sequence involving a burning house that takes off into the stratosphere, a flamboyant set-piece that makes little sense but does provide some needed spectacle in what’s otherwise a rather dour shoot-‘em-up.

It’s to the credit of the cast that they manage to keep a straight face while traversing this often ludicrous material. Winslet seems to have the most difficult time doing so, encased as she is in a tight blue dress that, together with an excess of shots from the rear, does not show her figure to best advantage; her default position seems to be a blank icy stare. Teller makes the most of Max’s cagey opportunism to garner a few laughs, but Elgort is a stick, and James little more than a handsome mannequin. Most of the heavy lifting is assigned to Woodley, who endures some extreme physical demands—like dangling from a bunch of electrical cords—while elsewhere scrunching up her face in an agony of grief. Let’s just say she comes in a distant second to Jennifer Lawrence. Watts gets what amounts to a cameo in this installment, though she looks to be a major player in the next one.

Technically “Insurgent” is a good, though not outstanding, piece of work by today’s tentpole standards. Florian Ballhaus’ widescreen cinematography is fine though awfully dark, and effects are more than adequate, even if they’re never as spectacular as they might have been. (The preview screening wasn’t in 3D, so the extent to which that format improves things—or merely further darkens the images—can’t be judged here.) Alec Hammond’s production design is similar to that of the first installment, and editor Nancy Richardson, teaming this time with Stuart Levy, brings the film in at just about two hours—appreciably shorter than the first picture, which is surely a virtue. The score by Joseph Trapanese (replacing Junkie XL) is generic, but effective.

If you get bored while watching “Insurgent,” you can always play the Erudite game, which simply involves counting which pronunciation of the word occurs most often. It appears that “er-yoo-dite” is the preferred version, though on occasion you’ll hear “er-ee-udite” and rarely “er-oo-dite.” You’d think that in a society to given to uniformity, somebody would have reached a definitive decision on this weighty matter. Maybe by the next installment.