The time period, somewhere in the not too distant future. Aliens have attacked and the humans are fighting back and not winning. This is all shown in an opening sequence that does a nice job of quickly laying out the facts.
This movie has been compared to Groundhog Day but unlike that classic movie, Cruise's character, Major William Cage, is able to keep advancing to the future as long as he doesn't get killed. (That, and there's a lot more violence and mayhem in Edge. Not so much in GD unless you count trying to kill the rascally rodent.)
Once Cage dies, he wakes up and starts all over again, as a private, about to launch an invasion. After the first experience, he realizes everyone in his unit will be slaughtered and the operation is a failure. He tries to warn the commanding officer, to no avail. Finally, one day during the invasion as he's trying to figure out a way to NOT die, he meets Sergeant Rita Vrataski, played well by Emily Blunt. She knows what's going on and the two work together to find and destroy the Omega, the brains behind the aliens. You can read a more detailed synopsis here: http://en.wikipedia.org/wiki/Edge_of_Tomorrow_(film)
What I enjoyed about this film was how, even though he is not trained for combat, Cage keeps using common sense to figure out how to avoid what killed him the day before. He also runs into many obstacles and has to determine what to do the next 'cycle', so the scenario is changed. How nice if we all had the chance to do this with our lives! Or, maybe not. Who's to say one path we take is better than another? Unless we're trying to save the world. In that case, I say we get as many chances as possible.
Enjoy this trailer and check out the movie in 3D.