Sean Baker’s low-budget feature is essentially a sleight-of-hand trick, withholding key information about the main characters in order to reveal it in moments of calculated surprise. Before the secrets start coming to light, this plays like any number of precious indie dramas, depicting the unlikely friendship between a pretty young stoner (Dree Hemingway) and a solitary old woman (Besedka Johnson) in lower-middle-class Los Angeles. Just when the story threatens to get mawkish, it turns dark; the effect is impressive, but it doesn’t quite validate the tedium of the first act, nor does Baker sustain its shocking impact for the movie’s remaining hour. Still, this is confident, engrossing storytelling, and the actors are terrific (particularly James Ransone, playing a loutish drug dealer).