Twenty-years in the future England is the only country that still has a civilization, primarily because it has blocked itself off from the rest of the world. There also hasn't been any children born in eighteen years, which has had quite a profound effect on mankind.
Theo Faren (Clive Owen), once a peace activist, is recruited by his ex-wife Julian Taylor (Julianne Moore) to help get a woman out of England. He learns that she's pregnant - and there are people who want to use her for their own political purposes. So it's up to him to get her to safety. Through their journey we're shown this plausible futuristic world.
CHILDREN OF MEN is well-shot and directed but it's a very dark, depressing film, so make sure you're in the right mood before you watch it. It reminded me of SOYLENT GREEN, which it has a lot of parallels to.