There comes a time in every franchise when it is best to leave well-enough alone. That definitive time in the "Terminator" series is fifth entry "Terminator Genisys." Not only rewriting the history of what has come before but rendering all four previous installments null and void, director Alan Taylor (2013's "Thor: The Dark World") and screenwriters Laeta Kalogridis (2010's "Shutter Island") and Patrick Lussier (2011's "Drive Angry") jerk the viewer around to such a degree that many fans will feel cheated. To dedicate oneself to an ongoing story over the span of thirty years only to be told, "Nope, none of that happened; this is what really happened," is a slap in the face, and not even the charismatic performers can save things. The similarly twisty but far smarter and more respectful "Back to the Future Part II," this is not.

In post-apocalyptic 2029 Los Angeles, resistance leader John Connor (Jason Clarke) sends dutiful protege Kyle Reese (Jai Courtney) back in time to 1984 to rescue John's mother, Sarah (Emilia Clarke), thereby ensuring that future savior John is born just as he should be. Kyle, who doesn't yet know he is John's father, aims to stop a cyborg (Arnold Schwarzenegger) programmed to destroy Sarah, but it isn't long before it becomes apparent that the new 1984 has radically diverged from the old alternate timeline. No longer a scared and confused waitress who needs saving, Sarah has been waiting for this day for nine years alongside her Terminator protector Pops (Schwarzenegger again). Their master plan is to travel to 1997 and destroy nuclear weapons organization Skynet before it has time to cause the so-called Judgment Day, but in this changed space-time continuum the fateful day zero is in 2017 as master operating system Genisys prepares to link up all of the world's technology. Once Sarah and Reese arrive in 2017 mere days before annihilation, the race to save the whole of humanity begins.

"Terminator Genisys" is too overplotted for its own good, at once cloyingly pleased with itself and seemingly dreamt up on the spot. Director Alan Taylor scarcely slows down—quite an achievement for a film where the characters spend most of their time explaining to each other what is going on while dodging bullets and liquid-metal robots—but technical proficiency in shooting action sequences doesn't stop the proceedings from quickly growing tedious. The hows and whys of the narrative are convoluted at best and downright nonsensically murky at worst, but the real offense is in realizing just how inconsequential and unnecessary its very existence is. Save for the novelty of seeing Arnold Schwarzenegger (2015's "Maggie") back in the saddle as an older but not obsolete model of his previous Terminator characters, there is no detectable reason why this picture was screaming out to be made. Entirely discounting what occurred in 1991's "Terminator 2: Judgment Day," 2003's "Terminator 3: Rise of the Machines," and 2009's "Terminator Salvation" while reimagining the events of 1984's "The Terminator" is a woebegone idea, plain and simple, and should never have made it out of the pre-production stage.

The "Terminator" movies have always been inconsistent when it comes to their actors—there have been no less than four different John Connors and three Kyle Reeses—but "Terminator Genisys" is nonetheless effectively cast. Jai Courtney (2015's "Insurgent") is a compelling replacement for Michael Biehn as the noble Kyle, gradually learning as he goes just how crucial his role is in their battle against Skynet's advanced machines. As Sarah, Emilia Clarke (HBO's "Game of Thrones") captures the youthful vitality of the younger Linda Hamilton from the original film with the transformative, no-nonsense toughness she brought to "T2." It is a successful medley, and Clarke has no trouble making the part her own without losing the spirit of Hamilton's work. Jason Clarke (2014's "Dawn of the Planet of the Apes") finds an intensity in John Connor that goes beyond Christian Bale's straight-faced growls in "Terminator Salvation," and where his presumably heroic character is taken is unexpected and decidedly anarchic—even if, again, it throws away everything one thinks he or she knows about him. J.K. Simmons (2014's "Whiplash") also pops up for a handful of scenes as O'Brien, a detective from their past, but the character's only memorable trait is that Simmons is portraying him.

"Terminator Genisys" toys throughout with alternate realities and nonlinear storytelling while sticking closely to its sanitized PG-13 rating; scenes mirroring ones in the R-rated first film do so by meticulously shaving off nudity and violence from the equation. A few action set-pieces are dynamically helmed, including one set on San Francisco's Golden Gate Bridge—officially the most overused landmark in recent disaster-movie scenarios. The most nagging issue with "Terminator Genisys" lies in its very conception. By going off on a fan-fiction-style tangent so wild that it discounts the events of "The Terminator" and its first three follow-ups, it becomes difficult to buy into or care about these characters' revisionist fates. Instead of being riveted by what is on the screen, there is a purveying feeling of audience annoyance not helped by the filmmakers' air of arrogance in dismantling and resetting the series up to this point. Sarah's ultimate discovery that she no longer is beholden to a predestined future and is finally free to live her life any way she pleases would carry with it a deeper emotional catharsis were it not cheapened by yet another distaff setup for a sequel. Unapologetic in its refusal to be held accountable for frivolously tossing aside all that has gone before, "Terminator Genisys" unconvincingly proposes the start of a brand-new trilogy. All involved needn't have bothered. This one has done enough damage.