"Rosemary's Baby" meets "Paranormal Activity" was very likely the initial concept that inspired 20th Century Fox—a studio not typically associated with found-footage horror—to take a chance on "Devil's Due." Directed by Matt Bettinelli-Olpin and Tyler Gillett, the duo also known as Radio Silence (2012's "V/H/S"), this apocalyptic tale of a pregnancy quite literally from hell is 80 minutes of foreboding deftness tucked inside a disappointingly aimless wraparound device. Genre pictures frequently seem to have a difficult time devising satisfying conclusions to their stories, in turn putting a damper on all the areas in which they excel. Bettinelli-Olpin and Gillett, along with aptly-named screenwriter Lindsay Devlin, fall into this infernal trap, unsure of where to take their characters and unwilling to delve as deeply and darkly as the despairing plot demands. When they get it right, though, "Devil's Due" cooks to a scalding boil, the filmmakers sending nervous viewers to their seat's edge while subjectively loading the narrative with tough themes dealing in the strains of marriage, having children, and being faced with uncertainty when one's best-made plans for the future are suddenly upended.

When Zach McCall (Zach Gilford) marries Samantha (Allison Miller), their ensuing honeymoon in the Dominican Republic city of Santa Domingo takes an unsettling turn when they are lured by their cab driver (Roger Payano) to a sketchy underground club where they eventually black out. When they awake the next morning, hung over but safely in their hotel room, they assume the cabbie kindly escorted them back at the end of the night. Returning to the United States, Zach and Sam begin to settle into their normal lives until a pregnancy test results in confirmation that they are having a baby. Sam is adamant she "took the pill religiously" (her words), but of course birth control isn't one-hundred percent effective, and what's done is done. As they start excitedly preparing for their first child, Zach cannot help but notice a change in Sam's personality. Faced with nose bleeds, sharp pains and extreme mood swings, she gradually becomes convinced something is grievously wrong with their unborn offspring. With strangers spotted lurking outside their home during all hours and hidden cameras set up by unidentified entities recording their every move, these newlyweds must find a way to put a stop to their doomed destinies as the birth of what might well be the antichrist draws near.

A purveying aura of paranoia and supernatural menace ramp up at a deliberately arresting clip in "Devil's Due," a spectacularly shot slow-burn suspenser incorporating recordings from various digital video cameras (most prominently, Zach's) with intermittent surveillance footage to piece together our lead couple's short-lived "family history." The brief prologue, finding Zach bloodied and shell-shocked during a police interrogation, should have been excised; because it is revealed that he survives his ordeal from the first frame, this needless knowledge threatens to steal some of the tension during the ghastly third act. Regardless, the film's descent into terror still packs a bit of a punch, from the eerie sense of dislocation present during the honeymoon to the increasingly suffocating stages of pregnancy as the malevolent figures around them close in. There are a handful of set-pieces both classy and appalling in equal measure, including a first communion gone awry and a freakish interlude where three young picnickers pay dearly for attempting to aid the wrong possessed figure who has been slaughtering deer in the area.

The supporting cast hanging around the fringes mesh plausibly with the film's cinéma vérité style, but it is Zach Gilford (2013's "The Last Stand") and Allison Miller (2009's "17 Again") who ably anchor the spectacular goings-on in an air of sympathetic levity. As Zach and Samantha, Gilford and Miller earn the time dedicated at the onset to set up and develop their loving relationship before their world as they know it inevitably topples down. It is important to care about a movie's characters enough to actively want to see them through to the end, and directors Bettinelli-Olpin and Gillett make sure that these two people gain the viewer's trust and concern even as Sam loses herself to demonic forces beyond her control. In a different picture that didn't involve black magic and an end-of-times omen, they would be looking at a blessed happily ever after. It's a shame about the satanic conspiracy with which they uncontrollably get involved.

"Devil's Due" relies upon dread over cheap scares, and for an extended period the film flies above and beyond the expectations of a cold-opening January horror release. There are the spare plot holes—when Sam, in one of her fugue states, terrifies her little niece during a family get-together, it is promptly swept under the rug without consequence—but they are relatively minor discrepancies within a greater tableau. A more nagging misstep is the step it doesn't take at all, ending in a way that could only possibly be satisfying in hindsight if there were a sequel. Since each film should stand on its own, it bears mentioning that this one gets cold feet at the last minute, pulling back and leaving things frustratingly open-ended. If the last three minutes aren't on par with the rest of the movie's uneasy fun, it is fortunately not a deal-breaker. "Devil's Due" stresses and dismays in the best of ways, all while bringing purpose and even tinges of innovation to the recently overused found-footage conceit. Any thriller that uses Brenton Wood's upbeat 1967 R&B hit "The Oogum Boogum Song" as its ironically sinister anthem is one that is thinking outside the box. That is an admirable place to be.