David Cross, best known as a comedian, turns in a thoughtful performance in “The Dark Divide.” Brent N. Clarke/Invision/AP

At the start of “The Dark Divide,” playing now at PMA Films’ online “virtual video store,” onscreen text describes Washington-Oregon’s vast Gifford Pinchot National Forest as “undeveloped,” “unexplored,” and “unprotected.” You might say those things about this indie marvel’s protagonist, real-life naturalist Dr. Robert Pyle, played with uncharacteristic sweetness by David Cross.

An expert on butterflies (“and moths,” as he likes to remind everyone), and not much else, Cross’ Pyle is first seen in extreme close-up, filthy, bleeding and seemingly nude, running in panic from something that’s breathing heavy and stomping along behind him in the darkness. When, flashing back to the start of what would become a weeks-long trek through the aforementioned wilderness, we meet Pyle in his more natural habitat, it seems only inevitable that this bookish, shy intellectual would end up on the wrong side of something huge and hungry should he ever venture away from the cozy house he shares with his more adventurous wife, Tia (Debra Messing). 

And “The Dark Divide,” a gentle, genuinely endearing biographical comedy-adventure-drama written and directed by Tom Putnam (a respected documentarian who – perhaps after some sort of head injury – once directed the infamously abysmal Paris Hilton vehicle “The Hottie And The Nottie”), does put Cross’ unworldly Pyle through some of the knockabout paces you might expect from that setup. (Owl on the head, falling into rivers and over cliffs, some pernicious bear poop.) But the film announces itself from its opening scenes as something more akin to the ever-overlooked 1983 indie classic “Never Cry Wolf,” also about an in-over-his-head naturalist (Charles Martin Smith as Farley Mowatt) whose field study of wolves sees him falling through frozen lakes and eating mice sandwiches, among other hardships, on his way to becoming a frontier-worthy protagonist.

For Cross’ Pyle, his unlikely journey into the Dark Divide (what the region’s Native peoples call the Gifford Pinchot), comes thanks to one last prod from his wife, seen in wrenchingly affecting glimpses of Messing’s Tia, dying painfully of cancer while the helpless Pyle can only look on in fear. The two actors, mainly noted for comedy, do tenderly funny work in their scenes, Cross’ flinching solicitousness toward his audacious wife’s desires to keep her wonted spirit until the end paired heartbreakingly with Messing’s knowing glances indicating her fears about her timidly loving husband’s life without her. Telling Cross on her deathbed about one last surprise she’s planning (in a lifetime undoubtedly filled with them), Messing’s final gift comes in the form of a coveted Guggenheim fellowship of $11,000 for Cross to finally document the Dark Divide’s rarest Lepidoptera — with the provision that he make the perilous, 30-day trek on his own. 

It’s, again, a setup that could have gone in for farce or cringe comedy, but Cross, hinting at Pyle’s bereft soul with admirable restraint, never succumbs to the absent-minded professor clichés, even as he starts out by making every rookie outdoorsman’s mistake in the guidebook. (There is a whisper of “Arrested Development’s” Tobias Fünke on a camping trip at the outset.) Putnam, filming Cross on location in the Divide’s impossibly lush, craggy, and unpredictable terrain has a way with wry visual jokes. A long shot of Cross tenderly testing out his brand-new gear in the wooded parking lot where he’s set to begin does a slow, lingering circle all the way around the thick, wet, surrounding brush and shadows until it returns to Cross, the eloquent punchline a simple recognition that Pyle has no idea what he’s in for. Another, following a particularly thrilling (and frightening) misadventure where Cross is lost in one of the forest’s impossibly old lava caves, is punctuated by one of Pyle’s elusive butterfly quarries fluttering unseen through the corner of the screen as Pyle lies (naked but for his underpants) panting in relief on the forest floor.

For what is, for most of its unendingly entertaining 107 minutes, a one-man show, Cross’ Pyle manages to run across some welcome souls in the woods along with him. Apart from gas station attendant Cameron Esposito (bemusedly certain that the map- and snack-purchasing Cross is walking right to his death), the increasingly bedraggled Pyle runs across unauthorized dirt bikers, a warily helpful young forest ranger (Peyton Dilweg), some surly and violent loggers (the film is set during the 1990s spotted owl conservation controversy), the loggers’ gruffly no-nonsense foreman (the great Canadian Native actor Gary Farmer) who shares some thermos coffee and a knowing counterpoint to Pyle’s theoretical conservationism, and maybe Bigfoot. 

Maybe.

Pyle, now known as much for his Sasquatch research as his world-renowned butterfly (and moth) expertise, keeps coming across hints to the existence of the legendary creature in his travels. There are those curious whoops echoing in response to his contented whistling after a successful dinner of caught fish. The Native son (Dyami Thomas) tells of his belief that it’s Bigfoot (Bigfeet?) that are trashing loggers’ equipment to protect the forest – and the mysteriously destroyed trucks at the logging camp that see the loggers set their sights on the innocent Cross. (Their depredations do send the defiant Pyle on an admittedly low-stakes bout of eco-terrorism, in a genuinely triumphant little scene.) Oh, and the print of what is, undeniably, a very big foot. 

Still, as tantalizing as those encounters are, “The Dark Divide” is a much more a character study of a grieving, seemingly helpless man who does, indeed, get the point of his late wife’s final, liberating joke. Plenty of movies posit the great outdoors as a cure-all for us city folk lost in our own unhappiness and isolation. (Reese Witherspoon in “Wild” comes to mind.) But “The Dark Divide” isn’t much interested in easy answers (to grief, environmentalism, seizing the day, etc.), instead giving Cross’ Bob Pyle a refreshing (and, again, very entertaining) brush with a world that, it turns out, is a whole lot bigger than he allowed himself to imagine. 

Not to draw too obvious an analogy, but longing to escape out into a bigger world after too long trapped in a stifling, soul-deadening, lonely, and sometimes frightening daily existence has its appeal right now, beyond “The Dark Divide’s” numerous cinematic attributes. Cross is simply terrific, toning down his innate smart-mouthedness in favor of inhabiting an odd but genuinely admirable man’s physical and emotional expedition into the unknown. And if the thought of one guy walking through the woods in search of butterflies doesn’t sound like much of a movie experience, well, you could probably use a walk in the woods yourself. Or at least a movie about one. 

It’s about the journey, isn’t it? And what you choose to do on the other side. 

“The Dark Divide” is screening online through the PMA Films “virtual video store.” A three-day screening ticket is $9.99 and, as ever, a portion of that goes right back to the PMA. 

Dennis Perkins is a freelance writer who lives in Auburn with his wife and cat.