The initial installment of “Maze Runner” was one of the better entries in the slew of movies adapted from YA novels about dystopian futures, and this follow-up proves its equal. “The Scorch Trials” won’t win any awards for originality, but it carries the familiar adventure along efficiently, generating sufficient excitement to keep one from dreading the next episode. That’s a considerable accomplishment, given that the second part of any trilogy is usually the most difficult to pull off.

The picture begins where the first left off—with that installment’s survivors in the supposedly protective care of the rivals to the World Catastrophe Killzone Department (known only by the acronym WCKD) headed by Dr. Ava Page (Patricia Clarkson), which had held them captive in the maze and is apparently devoted to finding a cure to a plague that has devastated humanity. Thomas (Dylan O’Brien) and Teresa (Kaya Scodelario), along with their Glader friends Minho (Ki Hong Lee), Frypan (Dexter Darden), Newt (Thomas Brodie-Sangster) and Winston (Alexander Flores) find themselves ensconced in a compound presided over by Janson (Aidan Gillen), a smugly officious fellow who smoothly assures them—along with the other youngsters in the dormitories, rescued from other mazes—that they’ll be sent off in daily groups to some sort of rustic paradise.

Although his friends are content, Thomas is justifiably suspicious of the set-up—especially as Teresa has been secreted away for some special medical treatment—and is helped by Aris (Jacob Lofland), a skittish inmate who’s been around awhile, to discover the compound’s real purpose. It’s an operation of WCKD, collecting young people who have demonstrated immunity from the epidemic and somehow draining them of whatever in their system provides their immunity, so that it can be used to cure others. Thomas then stages an escape from the facility, taking Aris along with his friends. This might be called the “prison break” section of the movie.

The outside proves extremely torrid and inhospitable, and the plot becomes a series of genre episodes. At first it’s a zombie movie, with our heroes endangered by the “Cranks,” crazed plague victims that apparently devour the few immune souls left around. Then it turns into a survival test with “Lawrence of Arabia” overtones as the crew must slog their way through a vast, hot desert—the titular “Scorch”—on their way to the distant mountains where, supposedly, a rebel army has taken refuge. An explosion of lightning forces them into a forbidding fortress where a group of mercenary scavengers headed by a Lando Carlrissian type named Jorge (Giancarlo Esposito) and his aide Brenda (Rosa Salazar) preside over a gaggle of brutish followers. Call this the “Mad Max” section of the movie, with our band of intrepid youth literally hung up to await a decision about their fate.

That takes us to the movie’s final segment, when Thomas and his followers—now including Jorge and Brenda—make their way to the remnants of the depleted rebel force, where they find former WCKD bigwig Mary (Lili Taylor) and troop leader Vince (Barry Pepper) preparing for a desperate campaign and Thomas learns details of his own past. Unhappily, a twist—unfortunately telegraphed from many miles away—brings the forces of WCKD against the ragtag crew, and when the fighting is over only a few rebels are left. Consider this the “Empire Strikes Back” part of the scenario, though the hardware is much more primitive. All seems lost, but that merely sets the stage for the grand finale that will be presented in the final part of the trilogy.

One of the pleasures of the original “Maze Runner” was that it eschewed the massive CGI that had overburdened so many pictures of this sort. “The Scorch Trials” follows that pattern: there’s some computer-generated imagery about, but much of the action is of the real person variety, and that’s a welcome change from the norm. The cast is agreeable, too. O’Brien has an everyboy quality about him that works in this sort of fare, and though Scodelario is rather pallid (a function of the role more than the actress), the rest of the youngsters are fine, with Lee showing off his physical skills to especially good effect, while the undersized Lofland makes a fine addition to the crew. The adults are more variable: Clarkson, in a one-note part not unlike the ones actresses like Meryl Streep, Glenn Close and Kate Winslet have played in other YA futuristic action films, is merely okay, with a characterization that doesn’t much go beyond her lovely white outfits. But Esposito brings the right note of roguishness to Jorge and Salazar welcome exuberance to Brenda, while Taylor manages to give nice warmth to Mary. And Gillen and Pepper are fine in more stock roles. All appear to respond well to the direction of Wes Ball, who also helmed the first installment. At 131 minutes, “The Scorch Trials” runs on rather long, but it’s more the succession of incident, rather than any lethargy on Ball’s part (or miscalculation on that of editor Don Zimmerman) that’s the cause. All the technical credits are thoroughly professional, and John Paesano’s score hits the right notes.

Like “The Maze Runner,” this sequel doesn’t set any new standard for this overstuffed genre, but it’s a solid, respectable adventure tale that’s old-fashioned in a good sense.