Here is a more detailed synopsis:
"Here's the idea in a nutshell: Predators have been using our planet for thousands of years as a training ground for their hunter-warriors. Aztec temples were the focii of this training, and Aliens were used as prey. The Aztec people saw the Predators as gods, and built many of their monuments for these hunters. The movie's choice of Aztecs seems strange, since their civilization only dates back a century before Columbus. If the producers wanted something old, why not the Olmecs, whose ancient civilization was the progenitor of later Meso-American empires? I guess Aztecs are just cooler.
At any rate, the Aztec Predators were wiped out by an out-of-control Alien infestation, and that was the end of that. But they also had an older, more secret temple buried under the icecap of Antarctica, where the training continued. Fast-forward to the present day.
The Main Plot
Charles Weyland, the billionaire industrialist, has discovered the Antarctic temple using thermal imaging satellites. Thinking that this could be the site of mankind's Master Culture, he assembles a crack team, Jurassic Park-style, to go take a look. What they find, instead of a manmade temple, is a Predator temple where five young hunters are about to conduct their first Alien hunt. The Predator weapon of choice is a six-bladed shuriken throwing star, while the Aliens use their trademark infest-and-impale method of fighting. The humans, of course, get caught in the middle of it. Movie tagline: "Whoever wins, we lose.""
From IGN.
