When the director Mélanie Laurent sat down to write Breathe, a psychological drama that was recently released in the U.S., she kept a photo of the 25-year-old actress Lou de Laâge on her desk. “Mélanie wanted someone who looked angelic but was a devil behind it all,” says de Laâge, a classically trained French theater actress, who plays Sarah, the antagonist in a destructive relationship between two high school best friends. “She is a manipulative narcissist but very well dressed!” When it comes to her own style, de Laâge epitomizes the effortless Parisian chic that is the stock and trade of brands like Vanessa Bruno, Isabel Marant, and agnès b. But then, such wicked beauty as hers doesn’t require much conjuring. De Laâge quips, “Eyeliner and a touch of lipstick—it’s discreet and not overwhelming."