“It Comes at Night” begins with a grim scare shot. An old man struggles to sit up and to breathe, some sort of wasting blight covering his bare arms and torso with lesions. A woman in a gas mask explains to him that he can stop fighting now; then a younger man and a teenager in gasmasks and thick gloves wheelbarrow the old man out to a canvas near a shallow grave in the woods. They shoot him in the head through a pillow, wrap him up, roll the body into the hole, douse it with fuel and torch the bloodstained heap. Billows of black smoke spew into the sky. Whatever the old man had, it’s clear they don’t want any sniff of it.
For a while, it seems that writer/director Trey Edward Shults (“Krisha”) is going to keep us suspended in this state of gut-churning dread. We learn almost nothing about why this family of three is holed up in a boarded-over house in the woods except that people in the city — which, exactly, is also kept vague — started getting sick. As the all-business father (Joel Edgerton) and mother (Carmen Ejogo) keep pushing ahead, Shults often comes to rest on the 17-year-old son (Kelvin Harrison Jr.), who mourns quietly, has a tendency toward insomnia, listens to conversations through the attic floor, and has terrifying dreams of people with all-black eyes leaking sludgy blood from their mouths. Meanwhile the violins in the pulsing score hold infinite, quavering notes, and even before anything much happens, you’re grinding yourself down into your seat.
Having built a perfect vehicle for horror, though, Shults stealthily moves to fill it with a survival thriller. One night an intruder tries to break into the house; the family captures him and ties him to a tree to wait out his possible symptoms. The visitor (Christopher Abbott) explains that he came in search of water for his family and that he has food to trade. Maybe they can broker a deal?
What follows is, in effect, a family drama with heightened stakes across the board. In its use of limited lights to peer into dark woods and down dark hallways, like a thing hovering just out of view, you get the sense that zombies might come kicking in the door at any moment, and it’s one you can never really shake. (The title is assuredly among the first things you’ll break down with your friends after the final credits roll.) Like other slower-paced post-apocalyptic stories — “The Road” comes to mind — the tensions in “It Comes at Night” center not on the world-changing event, but on the fallout. If you fancy yourself the type who would weather the immediate aftermath of a pandemic or a nuclear strike or an alien invasion, a fighter type, then congrats — you’ll see yourself somewhere in the tiny cast here. “It Comes at Night” forces the immediate question of “what then?” When you can’t leave the house, and the most dangerous people you know are in the house with you, all working to survive this thing?
The answer in “It Comes at Night” is open-ended. It winds up as the rare quasi-horror movie that feels entirely plausible. Fans of cheap jump-scares and bloated CGI might leave the theater disappointed; this isn’t how most creepy movies feel these days. But fans of patient, haunting thrillers will leave deeply spooked. And won’t look at their next nosebleed the same way.