"Allied" may be a calculating WW2-era romance, but it's hard to care when the film is so marvelously effective.

Allied, a World War II-era romantic thriller starring Brad Pitt and Marion Cotillard as spies from Canada and France, is a film with a split personality. In the first third or so, Allied plays like a conventional adventure-romance, something akin to Casablanca—and indeed the movie makes obvious references to the great Bergman and Bogart love story, such as the fact that it’s set in Casablanca in 1942. But then the film shifts in tone, becoming something darker and more somber for our spy-heroes, after fate twists their fake romance into a real one, and questions of nationality and loyalty become blurred in the name of love.

The movie opens with a hell of a shot: Brad Pitt, as Max Vatan, a Canadian spy working for British intelligence, parachuting onto the Moroccan desert. Pitt knows how to make an entrance, and the scene feels like something out of a James Bond. Upon arriving in Casablanca, Max quickly finds Marianne (Cotillard), who’s lunching with some French and German friends, all of them Nazi sympathizers. Marianne introduces Max as her husband, a character for whom Marianne has already amassed an array of details, even taking the time to furnish a wardrobe for him. Max is happy to play along, even beyond the typical calls of the job. That night, on the roof of their apartment, Marianne kisses Max, and the act of playing at love ignites the real thing. Of course, their mission also fuels their passion: Nothing binds two people together quite like assassinating a Nazi ambassador: Allied accepts the premise of every Bond movie that espionage is an aphrodisiac.

But Allied isn’t a James Bond movie. Director Robert Zemeckis, working from a script by Stephen Knight, goes for our emotional jugular, an act which is both cruel and satisfying. As a protegé of Steven Spielberg (who in his early career especially could transmute pop into art that moves us), Zemeckis instinctively wants to give us an emotionally big thriller, and the movie goes down some dark passages to fulfill that desire. Zemeckis lunges for significance with big themes and big emotions. You may feel like you're being manipulated, and yet, that may be half the fun.

Brad Pitt's performance jostles between effective and insufficient. At times he lacks the equipment to handle the emotional ups and downs of Max Vatan's life. However, at 53, Pitt is in terrific shape, and he's still convincing when he brandishes a machine gun or pilots an airplane or punches somebody's lights out. And to Brad Pitt's credit, he doesn't resort to histrionics, as though he were forcing himself into a more emotional performance, when a scene turns dark. Instead he turns stoic, like a pillar of marble. And maybe that's the right instinct of a star who knows his strengths and his weaknesses.

And then there's Marion Cotillard, dark and brooding, who also evokes that Old Hollywood star quality, and who has a vivid, almost palpable spark of life inside her. Cotillard commands our attention with those dark eyes and red lips and her somberly romantic expression: She can appear tragic even when she isn’t; she's alluring, deceptive, mysterious, like a modern-day Ingrid Bergman, so how could anyone--including Brad Pitt--resist her? In a sense, Pitt belongs in the first version of this movie, the one that keeps the tragedy of the war at an arm’s length; Cotillard, we sense, has been living inside the other movie all along, waiting for the tables to turn.

But the two work marvelously well together, fortunately, and even if Robert Zemeckis is a calculating director, meticulously assembling all the right elements, his stars twist the material back into something with heart. Zemeckis smartly knows that we must care about them in order to care about this movie. His calculations pay off, too, when the relationship between Max and Marianne collides into worldwide conflicts, like in a tense party scene at their home in suburban London, in which the city is besieged by a Nazi blitz, and a German fighter plane turns into an infernal torpedo and descends right toward their house. Never has the blitz felt more terrifying to someone who wasn't alive when it actually happened. And if Allied is calculating and cruel, it's also magnificently entertaining and, in the end, sobering.

With Jared Harris, Matthew Goode, Lizzy Caplan, Anton Lesser, August Diehl, Simon McBurney, and Camille Cottin.