Exactly which "night" is writer-director Trey Edward Shults alluding to with his teasingly enigmatic title? That "good night" into which Dylan Thomas implored us not to "go gentle"? The "Endless Night" to which William Blake informed us some are born (while others are "born to sweet delight")? The "Night primaeval" of Alexander Pope's "The Triumph of Dulness," a night signifying cultural apocalypse ("Art after art goes out, and all is Night")? Or — the most obvious possibility — the night of director George A. Romero's seminal work in which strangers take refuge in a fortified house to elude the living dead?

As it turns out, Shults' film in one way or another alludes tacitly to all of these. A nifty trick, given that It Comes at Night may well be the most minimalist horror movie ever made. The Krisha writer-director's second feature is an exceptionally tight, sly and, yes, heavy exercise in psychological suspense.

At first glance, you'll imagine you've spent time in this postapocalyptic milieu before in pictures like The Road. Something's unplugged the planet. Civilization has broken down. A mysterious, unstoppable plague is creeping closer. Inside a cabin in the woods, a family has barricaded itself against whatever the hell is happening outside. They are Paul (Joel Edgerton), his wife, Sarah (Carmen Ejogo), and Travis (Kelvin Harrison Jr.), their 17-year-old son. The story is told through his eyes.

Until recently, the clan had one more member. That was Sarah's father, Bud (David Pendleton). The first thing we see is Paul conveying Bud in a wheelbarrow to a shallow grave. He proceeds to shoot Bud in the head and set his body ablaze with gasoline, evoking the next line in Thomas' poem: "Old age should burn and rave at close of day." Bud raved, all right. He'd caught the virus. And we watch Travis watch his grandfather burn.

When another family presents itself and pleads for help, Paul is conflicted. Will (Christopher Abbott), Kim (Riley Keough) and their toddler, Andrew (Griffin Robert Faulkner), are eventually allowed to take refuge inside the rambling, boarded-up house. But Paul never allows himself to let his guard down, and a paranoid pressure builds with each ensuing scene.

Shults may be young — just 28 — but he displays the instincts of a master. He knows precisely which questions to leave unanswered and which dangers to leave unseen to create a credible, understated dystopia. I've been going to the movies for a while, and I don't believe I've seen a film as quietly unsettling. What's the worst thing that could happen? What could be more intensely unsettling than watching it happen to a loving family? Thermonuclear Armageddon can't hold a candle.

Revealing more about how the dynamic plays out would be unfair. It's enough to consider what planted the seeds of Shults' dark narrative. He's been candid when asked. The concept for It Comes at Night came to him in the wake of his father's death in 2014. Things are said in the film that the director actually said to his father at his deathbed.

Their relationship had been a troubled one, complicated by the parent's addiction issues. Shults has said that writing the script proved therapeutic and helped him process the loss. It's a stunning piece of work. In essence, Shults extrapolated the extinction of one man into that of the entire human race. He feels better now. It's time for the rest of us to have nightmares.