Lynn Shelton and Marc Maron Illustration by João Fazenda

In the writer-director Lynn Shelton’s new movie, “Sword of Trust”—her eighth feature—Marc Maron, the charmingly prickly comedian, podcaster, and actor, plays Mel, a charmingly prickly pawnshop owner and would-be musician. Shelton’s method, in “Sword” and three other films, makes use of improvised dialogue, and Maron, an incisive listener and an audacious conversationalist, is a natural improviser. “It doesn’t have to be an amazing guitar for somebody to have a great relationship with it,” he tells a hopeful seller, after rattling off a respectful but withering assessment of the man’s vintage Silvertone. (Maron contributes original music to the film.) Mel’s pawnshop, in Birmingham, Alabama, is full of items whose monetary and sentimental value are in close competition. Last week, before the New York première of “Sword of Trust,” Maron and Shelton visited a local storehouse of similarly sentiment-infused treasures: the Metropolitan Museum of Art.

The first stop was the Arms and Armor collection; they wanted to see some swords. As they entered a high-ceilinged grand hall festooned with ceremonial flags, which hung above a display of lance-wielding armored knights on armored horses, Shelton talked about the origins of the movie, which centers on a heavily mythologized Civil War sword. “I wanted to make a movie with Marc,” she said. “And I’ve always wanted to make a comedy caper where ordinary people get into a mess.” Mel’s caper involves a couple from out of town (Jillian Bell and Michaela Watkins), a Union sword that they inherit, and a band of pro-Confederacy conspiracy theorists who want to buy it. “I could see Marc in a pawnshop,” she said. “And it’s a good setting, because weirdos come in.” While writing at a friend’s place in Kentucky, she got the idea for a “problematic artifact” for Mel to acquire: a “prover item” for conspiracy theorists, which would bolster the veracity of a startling secret, long buried by the deep state, about the actual outcome of the Civil War. (“Seems like pretty big news,” Mel says, when he hears the story.)

Are there real sword-based conspiracy theories? Maron gestured at a suit of armor. “Arthurian legend,” he said, looking pleased. “Sure, he pulled it out of the rock.”

Shelton makes movies thriftily, shooting on location, with a tightly controlled number of actors, sets, and, possibly, costumes. (Maron and Mel dress very similarly, and Maron kept a pair of Mel’s cowboy boots, pawned by the Silvertone guy.) They shot the shop scenes in five days, in a corner of an actual pawnshop whose owner happened to own an inherited Union sword, which ended up starring as the MacGuffin. “I mean, it was the sword,” Shelton said. “It was crazy.”

“He didn’t want us to get our skin oils on it,” Maron said. In the movie, a potential buyer named Hog Jaws (Toby Huss) has a similar concern. Maron and Shelton strolled through several collections of antique ornamental swords. “You know what’s great about swords,” Maron said. “There seems to be a fair amount of consistency to the design. Long blade—”

“Pointy end,” Shelton said. She examined a hunting sword and knife. “It’s for stabbing boar,” she said, reading a plaque.

American swords were hard to find in the display—“Most of what’s American is guns,” a guard said—and, after examining a gold-inlaid circa-1853 Colt revolver engraved with patriotic motifs, suspended alone in a glass vitrine, Maron and Shelton continued on. In New Mexico, where Maron grew up, everybody had guns, he said: “First time I saw a gun was in high school. Guy had a .38. Showed it to me in art class.” They walked through the European Sculpture and Decorative Arts collection (“Lot of missing noses,” Maron said), Medieval Art, and Arts of Africa, Oceania, and the Americas. “I just read that Kurt Andersen book,” Maron said. (“Fantasyland: How America Went Haywire, a 500-Year History.”) “The place of fantasy and the compulsion toward it in the American mind is powerful. And that plays into the conspiracy theories, too.” In his standup act, Maron said, he “used to do a joke that there was a dogma to conspiracy theories, just like there is with religion.” He went on, “The joke was: If Jesus came back and said Oswald worked alone, you know there’d be people going, ‘That guy’s a patsy. He’s part of it! That guy came out of the sky! I’ve got facts on the ground! ’ ”

They approached another gallery. “My fantasy world involves the next exhibit,” Maron said. They entered “Play It Loud: Instruments of Rock and Roll.” “These are weapons I understand,” he said. He leaned over to examine Chuck Berry’s 1957 Gibson. “Semi-hollow body, with a couple of old humbuckers on it,” he said. “When I learned the beginning of ‘Johnny B. Goode,’ it was a big day.” ♦