The end is nigh in “Children of Men,” the superbly directed political thriller by Alfonso Cuarón about a nervously plausible future. It’s 2027, and the human race is approaching the terminus of its long goodbye. Cities across the globe are in flames, and the “siege of Seattle” has entered Day 1,000. In a permanent war zone called Britain, smoke pours into the air as illegal immigrants are swept into detainment camps. It’s apocalypse right here, right now — the end of the world as we knew and loved it, if not nearly enough.

Based in broad outline on the 1992 dystopian novel by P. D. James about a world suffering from global infertility — and written with a nod to Orwell by Mr. Cuarón and his writing partner Timothy J. Sexton along with David Arata, Mark Fergus and Hawk Ostby — “Children of Men” pictures a world that looks a lot like our own, but darker, grimmer and more frighteningly, violently precarious. It imagines a world drained of hope and defined by terror in which bombs regularly explode in cafes crowded with men and women on their way to work. It imagines the unthinkable: What if instead of containing Iraq, the world has become Iraq, a universal battleground of military control, security zones, refugee camps and warring tribal identities?

Merry Christmas! Seriously. “Children of Men” may be something of a bummer, but it’s the kind of glorious bummer that lifts you to the rafters, transporting you with the greatness of its filmmaking. Like Clint Eastwood’s “Letters From Iwo Jima,” another new film that holds up a mirror to these times, Mr. Cuarón’s speculative fiction is a gratifying sign that big studios are still occasionally in the business of making ambitious, intelligent work that speaks to adults. And much like Mr. Eastwood’s most recent war movie, much like the best genre films of Hollywood history, “Children of Men” doesn’t announce its themes from a bully pulpit, with a megaphone in hand and Oscar in mind, but through the beauty of its form.

It may seem strange, even misplaced to talk of beauty given the horror of the film’s explosive opening. For Theo, the emotionally, physically enervated employee of the Ministry of Energy played without a shred of actorly egotism by Clive Owen, the day begins with a cup of coffee, an ear-shattering explosion and a screaming woman holding her severed arm. The Mexican-born Mr. Cuarón, whose previous credits include the children’s films “A Little Princess” (1995) and “Harry Potter and the Prisoner of Azkaban” (2004), as well as the supremely sexy road movie “Y Tu Mamá También” (2001), has always had a dark streak. But nothing in his résumé prepares you for the shocking realism of this explosion, which proves all the more terrible because here it is also so very commonplace.