They don't make 'em like they used to, except when they do.

Allied, a journey to the past from Back to the Futuredirector Robert Zemeckis, isn't just a period picture — it's an anachronism. It's an unabashedly starry-eyed World War II thriller that thrives on the chemistry between actors so beautiful it hurts to look at them too long. It's so old-fashioned it actually originated as a screenplay (from Steven Knight, the British writer of Eastern Promises, Locke, and many others). It's so old-fashioned that it's rated R for sex. It's a mid-budget studio picture aimed at adults. It's a unicorn.

Set in Casablanca, London, and occupied France circa 1942-43, Allied relies heavily on CGI and greenscreens to place Marion Cotillard and Brad Pitt in these places as they existed 70 years ago. The good news is that Zemeckis, who has been tinkering with the storytelling possibilities of CGI for as long as that much-abused technology has existed, uses these tools to free up his camerawork rather than confine it. (The production also did some location shooting in the Canary Islands.) And if Zemeckis didn't also use his digital paintbox to youth-anize the 52-year-old Pitt's features by a decade or two, he's successfully created the illusion that he did. To gaze across the uncanny valley at Pitt's glassy-smooth mug in Allied is to recall that Zemeckis made a trilogy of motion capture movies in the aughts, proving (in The Polar Express) that even America's Reasonable Dad Tom Hanks could be rendered threatening through digital animation.

Although Allied looks to postwar thrillers like Notorious or The Third Man for its mix of glamor and grit, plot-wise, it feels mashed up from two prior Pitt movies: Quentin Tarantino's Inglourious Basterds,wherein he headed up a squadron of Nazi-hunting Jewish-American commandos, and Mr. and Mrs. Smith, in which Pitt and Angelina Jolie played assassins who are married but mutually ignorant of each other's odd profession.

This time,Pitt stars as Max Vatan — even his made-up name sounds old Hollywood — a Canadian airman who's part of the British Special Operations Executive. (Sadly, no one in the movie ever speaks this top secret outfit's more colorful name, The Ministry of Ungentlemanly Warfare.) A mission in Morocco requires Max to pose as the husband of resistance operative Marianne Beauséjour (Cotillard, radiant and enigmatic). In truth they've only just met and are under constant surveillance. The negotiations among these two smokin'-hot killers over how fully they should commit to their roles have all the sexual tension you're paying for, slightly dampened by Pitt's resemblance to a video game avatar.

This Casablanca-set first act burrows into the fine points of sustaining a secret identity: Marianne frets that Max's French accent pegs him as Québécois when she needs him to sound Parisian. A Nazi functionary switches tongues while quizzing Max on poker and chemical engineering, in an apparent effort to make him give away that he does understand English when his alter-ego does not. It's always fun to see how famous actors handle scenes in which their characters are acting.

Marianne and Max celebrate the success of their mission with a tryst in a car as it's being swallowed whole by a sandstorm. Zemeckis pulls his camera back and around the vehicle as it appears to dissolve into particles, a good example of how he uses digital trickery to show us something that probably couldn't be done any other way.

After that, Allied skips to London, where the two spies marry for real and take a house in bohemian Hampstead Heath. We're used to stories of how Blitz-hardened Londoners Kept Calm and Carried On; this one reminds us they also got high and had plenty of sex, keenly aware they could die at any moment. A scene of Marianne giving birth outdoors in the middle of an air raid feels more theatrical than cinematic, but this only deepens the the sense of grim absurdity that attends life during wartime. That Max's sister, played by Lizzy Caplan, is apparently in a relationship with a woman goes unremarked upon; the characters in this movie have bigger things to worry about.

The movie drops its other spit-shined shoe when Max's superior (Jared Harris, currently marching through this same decade as King George VI in the Netflix series The Crown), tells him the SOE has discovered a leak. The usually unflappable Max embarks an increasingly desperate series of moves — most spectacularly, an unauthorized night-flight across the English Channel to Dieppe — to try to prove his bosses' worst suspicions wrong.

Zemeckis' 40-year filmography includes work in almost every genre (and a directing Oscar for Forrest Gump), but he's made suspense films only rarely. That's too bad, because he shows a real gift for it, even if he lets things get a little mawkish in the final frames, as his contemporary Steven Spielberg is also prone to do. Not all of his gambits feel fresh: He scores a tense party scene at Marianne and Max's home with Louis Prima's big-band hit "Sing Sing Sing," a song song song that's been used in too many WWII-era films and TV shows (including the great WWII-set X-Filesepisode "Triangle") to have much kick left in it. Other period signifiers work better, as when Max peers over the top of a Graham Greene paperback at the wife he wonders if he truly knows.

Zemeckis doesn't let us see which Greene novel it is. I'm guessing The Confidential Agent,the movie version of which came out six months after the Nazis surrendered. It was sold on the chemistry between Charles Boyer and Lauren Bacall. They don't make 'em like that anymore, except when they do.

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