Aaron Katz’s Portland-set junior detective mystery stakes a claim as the founding work of mumble-noir. The 29-year-old director’s two previous features, Dance Party, USA (2006) and Quiet City (2007), established him as an offbeat miniaturist even by mumble terms. Exhibiting no particular rush to draw the viewer into its world, Cold Weather opens with college dropout Doug (Cris Lankenau) and his older sister, Gail (Trieste Kelly Dunn), with whom he now lives, preparing dinner for their parents. Having abandoned plans to become a forensic scientist, Doug takes a minimum-wage job at an ice factory by the railroad tracks, where he bonds with Carlos (Raúl Castillo), an aspiring DJ. The social network is complete when Doug’s ex-girlfriend, Rachel (Robyn Rikoon), returns to Portland on an undisclosed mission from Chicago. Carlos happens to have an extra ticket for a Star Trek convention; he invites Doug, who, elaborately uninterested, suggests that he take Rachel in his stead. She accepts but then disappears . . . We’re plunged into the world of mystery, although as Pacific Northwest enigmas go, Cold Weather is not exactly Twin Peaks. For the movie’s first half, the action is largely a matter of hanging out, something Doug is always happy to do. Steadily building in intensity from sluggish interest to mild excitement, Cold Weather is a slight movie with a long, circuitous fuse—and that’s the point. His movie is not a riff on mystery stories so much as it is a riff on the mystery of stories.