In Alfonso Cuarón's dank, hallucinated, shockingly immediate version of P.D. James's novel, humanity is facing its own extinction -- not through nuclear proliferation or global warming, but through the end of fertility. Like James's book, the movie opens with the violent death of the world's youngest person (18-year-old "Baby Diego," stabbed by an irate fan in Buenos Aires) and imagines what might happen if the human race were granted a miraculous second chance. The year is 2027, but the mood is late 1940. "The world has collapsed," a BBC newsreader explains. "Only Britain soldiers on" -- barely. The U.K. is a mecca for illegal immigrants, as well as a bastion of neo-fascist homeland security. London's smog-shrouded smear of garbage, graffiti, and motorcycle rickshaws is the shabbiest of havens. Armed cops are ubiquitous, and refugees are locked up in curbside cages. Clive Owen plays a wry and rumpled joker whose warmth is such that everyone trusts him, including a mysterious young woman (Clare-Hope Ashitey) who needs to be smuggled through the countryside. It's a measure of Cuarón's directorial chops that Children of Men functions equally well as fantasy and thriller as it attempts to fuse contemporary life with pulp mythology.