Ethereal Mathilde (Audrey Tautou), a provincial girl, cannot accept the disappearance of her beloved, Manech (Gaspard Ulliel), court-martialed under dubious circumstances for a mishap in No Man’s Land, the World War I abyss between front lines. Mathilde ignores her family and begins a personal quest for the truth. Along the way, she hires a detective and sees France through a strange carnival lens. Director Jean-Pierre Jeunet (“Le Fabuleux destin d’Amélie Poulain,” ”Delicatessen”) stirs up atmosphere and adds French-speaking Jodi Foster to his flashback-heavy, Fellini-like mix. But it is Tautou’s persevering innocence, like that of Emily Watson in “Breaking the Waves,” that makes this production both likeable and poignant.