“The only things to do down here are sweat and fuck,” we’re told not too long into Una Noche, a lyric-then-raw drama about a teenage brother and sister who scrape by in Havana, dream of Miami, and ultimately brave the 90 miles of Florida straits between the two. As they get their boat together, writer-director Lucy Mulloy honors—with great energy and even greater compassion—the sweat/fuck lives of the poorest residents of an island that has increasingly become a sex-tourism hot spot. A filmmaker of unstinting frankness, she reveals the harassment faced by young men and women alike, as well as the everyday business of body-selling, straight and trans, sometimes dwelling on the bodies themselves with a surprising tenderness—the prostitutes become people. We also see tourist dick, which to the Havana PD is just as sacrosanct as the tourist’s dollar. When he accidentally bloodies a white john, young Raul (Dariel Arrechaga), a restaurant worker pawed at by his supervising chef, knows that he now must leave the island before the cops get him. (Earlier, on the street, we hear a security guard bark to his superiors the authorities’ idea of a crisis: “There’s a citizen talking to a blonde.”) Raul, friend Elio (Javier Núñez Florián), and Elio’s sister, Lila (Anailín de la Rúa de la Torre), set out at last, and this urban slice-of-life becomes a tale of arguing kids, each touchingly preoccupied with his or her own sexual identity, all at odds with the elements themselves. The final, moving, nerve-wracking reels are all sea, sky, and desperation—and, oh, shit, is that a fin in the water?