Anyone expecting the movie “It Comes at Night” to live up — or, rather, to live down — to the self-consciously cheesy promise of its name, which hints at the kind of nocturnal boogeyman who has haunted so many horror films before it, must be unfamiliar with the work of its writer and director, Trey Edward Shults. That’s not surprising, given that Shults’s only previous feature, the family drama “Krisha,” was not widely seen, despite garnering several nominations and awards for the first-time filmmaker. With that 2015 debut, about an addict (Krisha Fairchild) attempting to reconnect with her estranged relatives, Shults demonstrated a flair for intense psychological confrontation — one that he puts into powerful new service in this work, a deeply creepy change of direction into genre moviemaking.

“It Comes at Night” will feel superficially familiar to fans of post-apocalyptic thrillers. Set in an isolated rustic home after some sort of plaguelike illness appears to have wiped out much of humanity, the movie focuses, with unflinching scrutiny, on the relationship between two small groups of survivors: Paul, his wife and their 17-year-old son (Joel Edgerton, Carmen Ejogo and Kelvin Harrison Jr., respectively) and the family they have welcomed, reluctantly, into their sterile, fortified refu­ge from contagion. The second family also features three people: Will (Christopher Abbott), his wife (Riley Keough) and their son (Griffin Robert Faulkner) — all of whom, like their wary hosts, appear to be free, so far, from whatever disease has ravaged the rest of the world.

Joel Edgerton, center, stars with Kelvin Harrison Jr., second from right, and Carmen Ejogo, right, as a father who, with his son and wife, merges with another family to hide from a contagion. As mistrust metastasizes, director Trey Edward Shults builds psychological terror. (Eric McNatt/A24 Films)

But these two camps know little about each other, and the disease, which any one of the visitors may have brought into the house without knowing it, kills rapidly and without warning. True to its title, much of the film takes place at night, when doubt, fear, nightmares and paranoia can be their most corrosive. Two of the characters — Paul’s teenage son, Travis, and Sarah, Will’s sexy young wife — suffer from insomnia. One of their scenes together crackles with sexual tension, of the sort that takes on new dimensions of danger, given that the method of the disease’s transmission is unclear.

Edgerton’s Paul has already shown himself to be impulsive, to a fault, setting up a situation — already fraught with unknowns — in which mistrust metastasizes into something much more terrible. As he did in “Krisha,” cinematographer Drew Daniels uses lots of handheld camera — this time lighting the scenes with lanterns and gun-mounted lights that swing this way and that, illuminating dark corners one minute and then leaving them in blackness the next. For much of its brisk running time, “It Comes at Night” teeters between delicious atmosphere and almost unbearable tension.

That may not be enough for some viewers who have been acclimated to expect the kind of payoff that often is accompanied by screaming and bloodshed in this sort of film — or the sort of film that certain parts trick you into thinking it might become, until it turns into something else entirely.

Oh, there’s plenty of mayhem at the climax. But the “it” that ultimately materializes, out of the movie’s shadows, may not be what you have been led to fear, even though it will be instantly, chillingly recognizable.

R. At area theaters. Contains violence, disturbing images and strong language. 97 minutes.