Cage (Tom Cruise) is a Army officer who works in public relations and media. He has no experience in battle, whatsoever. So when he pisses off a superior officer, is branded a traitor and forced to participate in a suicide mission against the invading aliens, he's scared crapless. He's killed--and then finds himself, back in time, to the instant he was at the army base. And then he's killed again and again. He encounters another soldier, Rita (Emily Blunt) who says to find her after he's killed next time. He does, and she explains how this exact same thing had happened to her. Because they both killed an alien "Alpha", it enabled them to take their ability to go back in time. Now, with this new weapon, they may have a chance of stopping the invasion.
If you crossed STARSHIP TROOPERS with GROUNDHOG DAY, this is what you'd get. Also, I was somewhat bored with all the action, that looked like an amalgamation of war scenes from THE TERMINATOR to the robot sentinels from THE MATRIX movies. Tom Cruises' OBLIVION is a far better science-fiction movie.