Christophe Honoré trades the whimsy of his quasi-musical “Paris Trilogy” for structurally ambitious psychodrama in Making Plans for Lena. Chiara Mastroianni is the 34-year-old title character, a single mom with the wardrobe of a college student and a responsibility allergy to match. Lena takes her two kids on a train trip to join her unhappily pregnant sister and blinded-by-young-love brother at the family’s country estate: Worn thin by familial expectations, Lena is already close to a meltdown when she’s forced to shoulder unexpected, unrelated visits from two men. Nigel (Jean-Marc Barr), the older husband Lena abruptly left upon discovering his mistress, makes it clear he’s there to see their kids and not her; Simon (Honoré mainstay Louis Garrel) is the lusty dreamboat who Lena once led on and then failed to follow through with. As soon as this contrast is set (Nigel representing the adult world Lena can’t hack; Simon, a temptation to slink farther away from it), Honoré takes a major stylistic leap, inserting a period film within the film, a brief fairy-tale interlude in which a girl with a bad reputation takes a suitor “to the local fete [because] before she married him, she wanted to see if he could make her dance for hours.” Honoré then follows Lena back to Paris, where she finds it no easier to keep time. After early similarities to current French films (particularly Arnaud Desplechin’s A Christmas Tale), Lena settles into a ’70s American groove, with Mastroianni making an all-in, glam-free performance look easy.