In 1974, a family of cannibals was slaughtered by vigilante townspeople in response to a brutal attack on some road-tripping teenagers. While most of the cannibals were killed, a baby girl was spared by a timely alien abduction. Growing up on a spaceship traveling at a significant fraction of the speed of light means that when she returned to Earth in 2012, Heather (played by Alexandra Daddario) was only about twenty while thirty-eight years had passed for the rest of us.
Of course, Heather's anti-aging secret didn't come without some adverse side effects. Growing up in a low-gravity environment robbed her of bone density and opportunities to develop coordination, so she tends to fall down a lot when trying to run in Earth gravity. Plus, her isolation in space prevented her from acquiring a normal set of social skills, so she now has bad taste in friends and is far too trusting of random hitchhikers and other complete strangers.
Mind you, this whole alien abduction subplot isn't explicitly spelled out in Texas Chainsaw 3D, but it's the only plausible explanation I can come up with for some of the otherwise glaring problems in the movie. And if her chainsaw-wielding, skin-mask-wearing older cousin Jedediah (aka Leatherface, played by Dan Yeager) had also been captured by aliens, then their advanced medical technologies could explain why he has no hint of a limp despite having almost lost his leg in a power tool mishap, and how someone who should be pushing sixty can keep up with or even outpace a bunch of much younger kids.
But like I said, we're spared any mention of this admittedly far-fetched outer space storyline. Instead, after being subjected to footage from the original The Texas Chainsaw Massacre vandalized by post-processed 3D, we're thrust into a present-day trip to check out a house that Heather has just inherited from relatives she didn't know she had. Unfortunately, it just happened to be the house in which the presumed-dead Leatherface had been quarantined (obviously, sometime after his return to Earth), and he would repay his unsuspecting liberator with an unpleasant death before turning his attention to the others.
As exciting as all this seems, Texas Chainsaw 3D is really not very good. None of the people in it are very likeable, so we don't have any sense of anxiety when they're being chased, nor any sense of loss when they're killed. Conversely, the shortage of gore and violence will live most horror aficionados unsatisfied (but to be fair, perhaps the absence of the word "massacre" from the title might have been intended to discourage such expectations). So we're left with a movie that isn't very exciting and that really doesn't benefit from giving the audience time to think about just how flawed it is.
It's kind of unfortunate that Texas Chainsaw 3D is the first wide release of the new year because it lessens the effect of calling it the worst movie of the year. But I think that it's bad enough that it will hopefully be able to hold onto that title for quite some time.