A strangely elegiac incest movie, Hungarian director Kornél Mundruczo’s Delta relies so heavily on ellipses and atmospherics that the viewer is left with the burden of parsing his sensitive subject matter. What’s surprising is that he almost pulls it off: On returning to his home village in Romania’s Danube river marshlands after a long exile, young shoe-gazer Mihail (Felix Lajko) exchanges two solemn looks with the fragile Fauna (Orsolya Toth)—one before he is told that she is his sister, and one after. Set on building his dream house far from prying humanity, Mihail is soon joined by Fauna, who seems eager to leave the dreary pub run by her affectless mother and overbearing stepfather. Mundruczo traces their progress with stunning beauty shots of the delta idyll and a controlled pace full of slow pushes and languorous pans. As the couple moves toward an arrangement that is against nature in nature’s pristine sanctuary (Mundruczo leaves their ultimate connection modestly concealed, as though it were beside the point), Mundruczo builds tension by asking us to define the terms of “natural” in a deeply disordered moral world. But the terrible reckoning that follows confirms Delta as most successful in exploring the terms of the dreary festival art film.