‘Sword of Trust’ is a beguiling, smart — and surprisingly deep — comedy

From left, Jillian Bell, Michaela Watkins, Marc Maron and Jon Bass in “Sword of Trust.” (IFC Films)

(3.5 stars)

There’s a low-key, lackadaisical charm about “Sword of Trust” that might lead viewers to mistake its modesty for lack of ambition. But there’s virtuosity at work in this beguiling comedy that’s no less impressive for being improvisational, understated and refreshingly self-effacing. There are no special effects, chase scenes or shootouts in this swift, compressed narrative, which clocks in just under 90 minutes and limits its action mostly to three locations, one of which is the padded back of a moving truck. The explosions in “Sword of Trust” occur by way of chemistry between the film’s four main actors, in their breezy and revealing banter and, in an extraordinary moment in the back of that truck, a breathtaking tonal pivot that sets the film on an entirely different and deeper course.

That moment belongs to the comedian and podcast host Marc Maron, who plays Mel, the owner of a Birmingham, Ala., pawnshop. In a revelatory performance, Maron brings his own smart, acerbic persona to a man who never intended to own a pawnshop. As “Sword of Trust” opens, he is dickering with a customer over what he’ll pay for a vintage guitar and a pair of boots, looking sarcastically askance at his doughy, perennially slack-jawed helper Nathaniel (Jon Bass), who is engrossed by the conspiracy-theory videos he watches on his laptop.

Mel, clearly, has seen it all, so when Mary and Cynthia (Michaela Watkins and Jillian Bell) come in to sell a 19th-century sword that belonged to Cynthia’s late grandfather, he isn’t particularly impressed. But they also bring in paperwork suggesting that the sword proves the South won the Civil War, a claim that Nathaniel is familiar with from the sites he visits on the Internet, where groups of amateur revisionists put out calls for “prover items” to bolster their loopiest theories: “What is this? ‘Antiques Roadshow’ for racists?” Mel exclaims when he sees a typical video.

Soon enough, the foursome are in the back of that truck in an ad­ven­ture that begins as a moneymaking scheme and promises to become a heroic journey into the heart of white supremacy at its most virulent and addle-minded. “We’re in the brain of that,” Mel exclaims excitedly while they bump along in the truck. “And apparently it’s carpeted,” Cynthia replies, taking in the swatches of brown shag that surround them.

Directed with easygoing assurance by Lynn Shelton from a script she co-wrote with Mike O’Brien, “Sword of Trust” joins such Shelton classics as “Humpday,” “Your Sister’s Sister” and “Laggies,” bursting with the same humor and intelligence as those films and evincing a shrewd eye for casting actors who can spin improvisatory riffs into pithy, observational gold. “Sword of Trust” is a perfect comedy of manners for our post-truth age, when historical consensus has become subject to the same kind of interpretive haggling as the price of a kitschy cream pitcher. (“The world is round,” Cynthia tells Nathaniel when he begins to spout the flat-earth party line. “Yeah, but, is it really, though?” he retorts.) In the hands of this gifted ensemble, “Sword of Trust” isn’t content simply to poke fun at the rednecks and rubes who believe in the most outlandish lies, but saves its best laughs for the foibles of the ones doing the ridiculing.

Things take a number of surprising turns as the group’s pursuit of the truthers and their money becomes more perilous and improbably amusing. But by far the most unexpected development is when Mel recounts just how he got to that Birmingham pawnshop, in a monologue that Maron delivers with breathtaking poignancy. Like all of Shelton’s films, “Sword of Trust” is dependably funny and a showcase for some splendidly nuanced comic turns, but in its final moments it becomes something more: a wistful testament to the people we can’t help loving, the people we love and can’t help, and the crucial work of drawing boundaries between them.

R. At Landmark’s E Street Cinema. Contains coarse language throughout. 89 minutes.