The would-be emotional horrors at the center of Chris Gorak’s “Right at Your Door,” a calculated descent through various stages of despair, are undermined by a far-too-rigid premise: Amid the hustle and bustle of a morning commute in Los Angeles, a series of dirty bombs are detonated, releasing a toxic cloud of ash that rains down over the landscape, threatening to kill 10 million people.

In the old days — pre-2001 let’s say — the dark allure of a nuclear bomb disaster flick would revolve around the horrific sight of a mushroom cloud, the carnage at the epicenter, and the hysteria of those who believe they’ve lost someone in the attack. To the contrary, what’s most interesting about Mr. Gorak’s film is the way his vision has been updated for the post-September 11 worldview. Far less interested in the up close horrors than in the distanced sense of panic embroiling the suburbs, the movie is preoccupied with such things as malfunctioning cell phone networks, the hoarding of plastic sheeting and duct tape, and a deep-seated sense that the government will be just as clueless as the public when the dark day has arrived.

Leading the way here are two characters firmly entrenched in today’s technology-obsessed, know-everything-now culture: Lexi (Mary McCormack) and Brad (Rory Cochrane), whom we meet as they play out their boring morning routine. Lexi gets ready for work while Brad, seen here against an array of electric guitars and amplifiers, listens to the morning news and gives her driving tips to avoid the clogged interstate. She heads off to work, he sets to showering and brushing his teeth, and that’s when the radio comes to a screeching halt in the form of the emergency broadcast system.

As vague radio reports of explosions merge into terrified first-hand accounts from reporters dialing in via cell phone, the size and scope of the attack comes into focus: Large bombs — set off along the highway, amid downtown, and at LAX — have released waves of radioactive toxins into the air. Terrified, Brad grabs his cell phone, then his landline, and desperately dials his wife. But of course the circuits are busy, so he hops into his car and tries to sneak past the various police roadblocks.

It’s when he goes off-roading and after he blows a tire that Brad begins to realize how dire the situation has become. Looking for a tire patch in a hardware store, he watches in astonishment as a woman grabs every roll of duct tape she can find. When it dawns on him that the attack has only just begun, he grabs his own supplies, races back home, and starts sealing up every window and door.

Given how often the radio reporters repeat the mantra, it’s easy to see where this story is headed: “Do not give medical help to those hurt by the blast,” the radio repeats. “They must be quarantined.” That, of course, is right about the time Lexi returns home, bloodied and coughing, and Brad is faced with the unthinkable moral dilemma.

Filmed dispassionately by the first-time director, who uses an ill-advised documentary approach that puts the camera in the seat next to Brad as he navigates the highways and next to Lexi as she paces outside the front door, it’s remarkable that Ms. McCormack and Mr. Cochrane are able to build coherent characters under such impossible acting conditions. For the first half of the film, Brad is effectively alone, and during the second half, he engages in some of the most emotional conversations with his wife imaginable — all while talking through layers of glass and plastic. Lexi, too, is cut off not just from Brad but also from her family members, who repeatedly calls her cell phone, leading to not one but two death speeches between Ms. McCormack and a piece of plastic fastened to her ear.

Clearly Brad is haunted by the decision he faces, about whether true love means dying with his beloved or if it means staying safe to ensure she gets the help she needs. But in separating them the way Mr. Gorak does, the agony is uninvolving and, at times, unbelievable. As an intellectual exercise, “Right at Your Door” has some chops — as a meditation on what it would take to survive when your beloved is the biggest threat to your survival, and as an examination of how radioactive fallout will reap just as much damage as the initial blast radius.

But there’s not much space for tangible, human interaction within this framework. Essentially, there are two emotional decisions to be made: Will Brad keep driving to find Lexi? And, when she returns, will Brad let her inside the house despite the danger? Once those bridges are crossed, we’re at a narrative dead end, and the story devolves into a loop of fear and anger.

One is reminded of Nevil Shute’s “On the Beach,” a story about a band of Australians, the last people on Earth, awaiting the arrival of a radioactive cloud drifting around the planet after a civilization-ending nuclear war. Hand in hand, they confront Armageddon, and perhaps “Right at Your Door” is the modern, haunting twist to that concept. Mr. Shute envisioned the end of the world coming not with a raging bang, but with a resolute whimper. Mr. Gorak clearly sees it as a free-for-all. Forget governments, marriages, or going bravely into the great beyond. It’s every man for himself.