The center of the film involves the journey toward the coast, which Faron and Kee undertake with Julian, Luke and Miriam (Pam Ferris), who is both watchdog and nurse. Along the way, they are pursued by Homeland Security troops, and there is a chase scene with one of the most sudden and violent moments I have ever seen in a film. Not all of the chases in all of the Bournes equal this one, shot in a single take by one camera, for impact.

Here again, the action scenes seem rooted in sweat and desperation. Too many action scenes look like slick choreography, but Cuaron and Owen get the scent of fear and death, and nobody does anything that is particularly impossible. Small details: Even in the midst of a firefight, dogs scamper in the streets. Faron's hand reaches out to touch and reassure the nearest animal, and I was reminded of Jack London's belief that dogs (not cats so much) see us as their gods. Apparently sterility affects only humans on Earth; when we are gone, will the dogs still tirelessly search for us?

I have been using Hitchcock's term "MacGuffin" too much lately, but there are times when only it will do. The lack of children and the possibility of children are the MacGuffins in "Children of Men," inspiring all the action, but the movie significantly never tells us why children stopped being born, or how they might become possible again. The children-as-MacGuffin is simply a dramatic device to avoid actual politics while showing how the world is slipping away from civility and co-existence. The film is not really about children; it is about men and women, and civilization, and the way that fear can be used to justify a police state.

I admire that plot decision. I would have felt let down if the movie had a more decisive outcome; it is about the struggle, not the victor, and the climax in my opinion is open-ended. The performances are crucial, because all of these characters have so completely internalized their world that they make it palpable, and themselves utterly convincing.

Cuaron fulfills the promise of futuristic fiction; characters do not wear strange costumes or visit the moon, and the cities are not plastic hallucinations, but look just like today, except tired and shabby. Here is certainly a world ending not with a bang but a whimper, and the film serves as a cautionary warning. The only thing we will have to fear in the future, we learn, is the past itself. Our past. Ourselves.