Vietnam War literature is where we first heard the combat infantry expression “thousand yard stare.” It’s entered the war lit/war film lexicon as shorthand for the soldier whose eyes reflect the exhausted wariness of anybody too long “in country.”

But it wasn’t until I saw Jesse Gavin wear it as a Afghan combat vet who will never get over what he lost in “Northern Shade” that I got a sense of what it must look like.

Gavin, a career bit-player turned leading man, gives a breakout performance as an infantryman who saw a close friend die overseas, and comes home to his old man’s boat — a weathered sport fishing trawler which he lives on — a strained relationship with his mother, a long-estranged younger brother, and a bottle.

If you saw, smoked with and chatted up the ghost of your fallen comrade Noel (Alejandro Bravo) on a regular basis, you’d drink, too.

When a private eye (Titania Galliher) visits The Gasshole — perfect name for a boat with no sails, BTW — and asks questions about a now-burned-out vehicle Justin gave his little brother Charlie, Noel chides Justin about his responsibilities.

“Go up there and find him.”

“Up there” is Connecticut’s rural border country with New York. Charlie’s joined some guys holed up in the woods. Yeah, it’s what you think. Yes, another guy “in the woods” is someone the private detective is looking for. And no, the cops — even the ones not sympathetic to camo-wearing secessionist militia goons — are not interested.

Writer-director Christopher Rucinski doesn’t stretch the genres he’s mashing up for this classic “find my missing partner/relative/lover/old-comrade” quest. His background is visual effects, but he’s made his writing and directing debut a film that doesn’t call for any, just really good actors.

What he gets absolutely right, in every role, is casting. Bravo makes a “careless” and somewhat naive Noel in the field, a weary best friend/nagging conscience as a ghost. Galliher is believable as an ex-military/ex-cop with a conscience. And Rose Marie Guess gives Noel’s war widow and single mom a pandemic-strained loneliness that’s easy to buy into.

The militia members we meet are belligerent, secretive and intellectually weak enough to fall under the spell of Billy (Romano Orzari), a strutting, conspiracy-minded blowhard and Wit and Wisdom of Joe Rogan philosopher.

“When elephants fight, it’s the grass that suffers. Somebody’s got stand up for the grass.”

And Gavin gives a John Hawke in “Winter’s Bone” eye-opener of a performance — haunted, twitchy, weary and guilt-ridden, a man who must lose that “thousand yard stare” before he can be of any use to anybody.

The plot points aren’t the most surprising or even rationally defensible. But Gavin & Co. make this an intimate thriller with personal agendas, limited people making rash, limiting decisions with life or death consequences, with no one there to talk them out of any of it.

Rating: unrated, violence, sex, profanity

Cast: Jesse Gavin, Titania Galliher, Rose Marie Guess, Alejandro Bravo, Joseph Poliquin and Romano Orzari

Credits: Scripted and directed by Christopher Rucinski. A Bayview release.

Running time: 1:36