These two poetic essays by Lynne Sachs offer the perfect antidote to PBS: there’s no omniscient narrator talking down to the viewer, reciting facts and explaining what to think, yet the story of each is perfectly clear. Investigation of a Flame examines the Catonsville Nine, who in 1968 stole records from a Maryland draft office and set fire to them with homemade napalm. Brothers Phil and Dan Berrigan, who led the protest, appear both in the present and in archival footage, a mix that makes their commitment palpable, while images like a newspaper going in and out of focus remind us that shifting contexts alter our understanding of complex events. Which Way Is East: Notebooks From Vietnam (1994), which Sachs made in collaboration with her sister Dana, is an impressionistic diary of their travels through Vietnam. They focus on the war, noting bomb craters and visiting the tunnels where a local woman says she lived for 20 years; in contrast, the Vietnamese they encounter seem more interested in the present. The sound track features the voices of both the filmmakers and their subjects, and traditional Vietnamese sayings (“When you share someone’s sadness, you lessen it”) help to shape the sisters’ musings in this intermingling of historical contradictions and very different cultural attitudes. 78 min. Sachs will attend the screening. Gene Siskel Film Center, 164 N. State, Thursday, September 20, 6:00, 312-846-2800.