Bryce Dallas Howard, left, as Kate Connor, and Christian Bale as John Connor, are fighting for their lives in the sci-fi action film, Terminator Salvation.

Warner Bros.

Six years after Resistance leader John Connor survived the last onslaught of the robotic killing machines that were sent from the future to kill him before he could destroy them in Terminator 3: Rise of the Machines, he’s back in Terminator Salvation to prove there’s still a lot of life — and room for mega-colossal special effects — in a series that refuses to die.

The moviemakers have upped the ante, replacing Nick Stahl from the 2003 movie with Christian Bale, who may have hung up his Batman togs to play Connor, but not his daredevil feistiness.

And they’ve added a new character, Marcus Wright (Australian actor Sam Worthington), a worthy antihero who dies in 2003 on death row at the start of the film, but somehow mysteriously reappears intact in the post-apocalyptic world of 2018 after the machines have all but decimated humankind.

The charismatic Worthington deftly takes center stage for nearly the entire first half of the film. For although Bale is introduced as John Connor in a thrilling early sequence that involves an A-bomb blast and a knockdown battle with a Terminator, he soon becomes a distant character who barks orders from the Resistance’s underwater headquarters. (Fans of previous films know Connor was fated to lead the rag-tag Resistance against the worldwide tentacles of machine-based Skynet and its army of Terminator robots, even before his character was conceived in director James Cameron’s 1984 original.)

The first film turned Arnold Schwarzenegger into a major international star and his famous line — “I’ll be back” — became part of the lexicon. It reappears in Terminator Salvation, although it’s not delivered with the same force. Schwarzenegger starred as the title character in the previous three films and, has a magic moment in Terminator Salvation, perhaps a precursor of a plot line for Terminator 5 which already is in the works.

Terminator Salvation was written by partners John D. Brancato and Michael Ferris, who did T3, and who give the latest a heavy concentration of the high-octane special-effect thrills that have become a trademark of the series. They’re carried to hang-onto-your-seats mind-bending heights by the director known as McG. He did the Charlie’s Angels films, so there is more than a carryover hint of the playfulness of those films in TS.

But McG also did the weepy college drama We Are Marshall and so maintains the depth of feelings of the characters that is an important part of the TS script. TS is more than just a fiery let’s-stop-the-Terminators adventure. It goes beyond merely good guy-bad guy terms. In it, Connor comes to reassess his thinking about the cyborg creatures and eventually must redefine what it is to be human. Pretty heady stuff.

Alas, however, the plot is more than a little complex, at least if one stops to think about it. Time travel must be involved — remember the original Terminator and the ones that followed came from the future — but the idea is never expanded upon or well explained here. Thus, Connor searches for Kyle Reese, the man who would become his father and who was played by Michael Biehn in 1984, but here is played by Anton Yelchin who is a good 15 years younger than Connor himself. Brancato and Ferris provide few clues as to exactly how this came to be. If one applies too much logic to the film’s ending, one may conclude that it’s simply impossible … save for the fact that it could be a jumping-off point for the next film.

But then the filmmakers are counting on people not spending too much time analyzing the plot, but just going along with the flow. Fortunately, it’s quite a rip-roaring ride.

By the second reel, Marcus is roaming the blighted landscape of what once was Los Angeles, not yet totally comprehending what was involved in the war the machines waged against the humans, but finding refuge with two Resistance fighters in the rubble — a young Kyle Reese (Yelchin) and a little girl (Jadagrace).

The three eventually flee to what they think will be a safer place, but along the way run into what becomes one of the film’s most exciting sequences in which they are attacked by a gigantic Terminator cyborg. Vehicles explode around them as they flee across a desert road littered with destroyed cars and trucks, chased by a pair of cyborgs on zooming motorcycles. It’s a demolition derby of mayhem, ending with some of the Resistance fighters snatched up by a flying saucer-like transport and whisked to certain doom at Skynet headquarters.

There are cyborgs who live in rivers and leap out to snatch the unwary and a thrilling airborne chase that owes much to air battles in World War II movies and to the assault on the Death Star in the first Star Wars.

Marcus is central to the air fight action, leading him to join up with a downed fighter pilot (vivacious Moon Bloodgood) who is charmed by his can-do determination. But just when she’s feeling cozy, a shocking surprise awaits both of them as well as Connor when they are united at Resistance headquarters. It changes the equation of the movie, although one may have guessed it ahead of time.

Bale comes into his own beyond his character’s action persona in TS. He has a very strong moment as Connor makes an impassioned plea to call off a battle that threatens to cost the lives of innocents. He also shares a heartfelt moment with Worthington that puts the whole human-cyborg equation into question.

Those who haven’t seen the previous Terminator films may be lost, at least for a time, because of all the ins and outs of the plot. Even those who have seen the earlier films, but not lately, will have questions.

Yet for big-screen excitement with lots of explosions and spectacular sights, Terminator Salvation is definitely the summer “popcorn picture” to beat.

****Terminator Salvation

Starring: Christian Bale, Sam Worthington, Moon Bloodgood, Helena Bonham Carter, Anton Yelchin, Jadagrace.

Rated: PG-13, contains violence.

mjanuson@projo.com