Sound of My Voice (2011) on Netflix

Plot summary

Peter Aitken is a substitute teacher in Los Angeles, and his girlfriend Lorna Michaelson is an aspiring writer. Together they make a documentary about a secretive cult, hoping to expose its leader as a fraud. Once deemed ready, they shower and dress in white surgical gowns, then are driven blindfolded to a basement where Klaus receives them with a practiced handshake. Inside, eight other members gather around Maggie, who breathes from an oxygen tank and says strict hygiene protects her from a severe illness. Maggie says she is from the year 2054, sent back to select a group that will prepare for war and famine. She leads the members through intense psychological exercises, and Peter and Lorna feel their skepticism wavering.