Underdeveloped premise not easy to endure

You can watch “It Comes At Night” straight through and never know exactly what “comes at night.”

Perhaps “it” refers to the fatal illness that’s ravaging the world and seems to have destroyed civilization. Or maybe “it” refers to something else — perhaps people who show up at night or bad things that happen at night.

In any case, the apocalyptic thriller reveals not the apocalypse but the world that arises immediately after it.

The people remaining don’t quite know what happened, just as passengers on a crashing airplane don’t know precisely what went wrong.

Taking stock, knowing things, weighing evidence — these are all the products of calm reflection, of breathing room, of a safe space for people to think.

In “It Comes at Night,” no such space exists.

As a portrait of what it might be like after the whole thing collapses, after systems carefully designed over centuries give way to bad luck or colossal stupidity, “It Comes at Night” is pretty convincing. Food and water are at a premium, and people retreat into their families and trust no one else.

There’s one notable problem, though: “It Comes at Night” is about as enjoyable for the audience as it is for the people in the movie. On both sides of the screen, misery reigns.

Joel Edgerton and Carmen Ejogo are husband and wife, and Kelvin Harrison Jr. is their 17-year-old son. They are holed up in a big house in the woods. They have access to water. They have guns. They have locks on entrances, with every window boarded up.

One day — at night, of course — a man (Christopher Abbott) breaks in, and the family must take defensive action.

That’s the initial event, and the story builds and expands from there — but not by much.

To the extent that “It Comes at Night” is a mystery, it remains a mystery. It depicts the characters’ predicament reasonably well, although the loud, noisy soundtrack is more annoying than pulse-pounding.

But it doesn’t venture far beyond the premise.

The film, written and directed by Trey Edward Shults, represents the second time in the past few weeks that a film with a lone writer-director has run into the same difficulty.

Like Robin Swicord’s

It’s not unreasonable for an audience to be interested in such questions when that interest is generated by the film itself. In the absence of such answers, “It Comes at Night” begins to seem thin, a torment without purpose.

The characters might be stuck in the world of the movie, but we’re not. We can leave.