William Earl SPOILER ALERT: This article discusses plot points in “No One Will Save You.” Horror Film School is a new feature in which talent in front of and behind the camera share the ins and outs of creating the biggest onscreen scares. “No One Will Save You,” out Friday on Hulu, is an incredibly lean genre movie: Aliens come down and invade the house of reclusive loner Brynn Adams (Kaitlyn Dever), and she must defend her property and warn her small town that extraterrestrials are trying to assimilate. Writer and director Brian Duffield pulls off two difficult things in his creature feature: The characters speak very little dialogue, and the aliens stalking Brynn are seen early and often — and they’re actually scary.