"It's not found-footage," says writer-director Adam Green (playing himself), "it's footage-footage." Having already created the "Hatchet" franchise, a slasher series revolving around a grotesque, murderous boogeyman who roams the Louisiana bayou, Green has opted to make a documentary exploring the public's fascination with onscreen monsters and villains. Interviews with artists, producers and actors largely picked up on the horror convention circuit take an unexpected turn when the filmmaker receives a fan letter from retired police detective William Dekker (Ray Wise), who claims he has first-hand knowledge that monsters are, indeed, real. Self-aggrandizing but undeniably effective, "Digging Up the Marrow" blurs fiction and reality by introducing otherworldly elements into a version of Green's everyday life.

Audiences in 2015 are more sophisticated and jaded than they were when "The Blair Witch Project" came out in 1999. Because it is a lost cause—and rather tacky—to pass off today's faux docs as actual footage, the director twists the formula by pulling himself into a reality that is honest in some ways and fabricated in others. Obviously, the casting of recognizable veteran actor Ray Wise (TV's "Twin Peaks," 2013's "Big Ass Spider!") as William Dekker betrays the aura of authenticity, and yet because Green is portraying himself and cinematographer-costar Will Barratt's camera follows him home and to his offices at production company Ariescope Pictures, it is easy to get wrapped up in the film's meta veneer. What is a little more shameless is the self-congratulatory air the movie emits, with parts of it wading too deeply into promotion of Green's filmography and brand (even Kane Hodder, in a cameo, pops up brandishing a "Frozen" T-shirt—one that has nothing to do with Scandinavian ice princesses). He is such an enthusiastic, well-spoken personality that this sprinkle of egotism can be overlooked, but it is there, and on occasion the plot at hand must take a backseat to it.

True to form, Ray Wise is never less than compelling, leading one to wish he received lead roles more often. Dekker is eccentric and possibly unhinged, but when he makes a case for the existence of monsters—really human beings born with physical deformities who were brushed aside by society and now make their home in an underground metropolis called The Marrow—he says it with such conviction that it almost sounds plausible. The particulars of where this story leads mimic that of a twisted, scare-laden (but not violent) funhouse ride, with Dekker, Green and Barratt staking out Rocky Pointe Natural Park after hours in the spot where Dekker claims an opening in the ground is the monsters' portal to our world. The suspense that builds in these segments is palpable, and Green (as director) is ace at absorbing the viewer into his web and then attacking. A handful of serious frights are delivered, the kind that cause audible gasps and leaps out of one's chair.

"Digging Up the Marrow" features a cool premise and, at its best, overtakes with its mounting fear—and curiosity—of the unknown. The creatures, inspired by the artwork of Alex Pardee and designed by Robert Pendergraft and Aunt Dolly's Garage, are unlike anything seen before on film, and the film gains extra mileage from setting them up early on via Dekker's first-hand drawings. They are fortunately worth the wait, going a long way in smoothing over the missed opportunity of the third act. By not exploring the world of The Marrow further, the film leads to a shrug-worthy conclusion that is neither fully developed nor realized. What endures, though, is Adam and his creation of a documentary that takes him down a path he can barely comprehend. "Digging Up the Marrow" could have used another polish on the screenplay level, but there is a cleverness to its conception and warranted confidence in its tension that cannot be refuted.