James Gray's The Lost City of Z, a turn-of-the-20th-century jungle trek through uncharted Bolivia, opens on a black screen and the pounding of primal drums. It's the sound of exoticism echoing from a lineage of Hollywood clichés that includes naked primitives, piranha attacks, quicksand, and bones through the nose. But when the picture blinks on, Gray's pulled a prank. The drums belong to British officers war-whooping a fox hunt, their own brutish tradition. Barbarism is universal.

Our star rider is Percival Fawcett, played by Charlie Hunnam in a wilting blond mustache that belongs on a Percival Fawcett. During the chase, the ambitious young soldier goes his own way — metaphor alert! — and wins the competition, not that it does him or wife Nina (Sienna Miller) any good. Percy has "been rather unfortunate in his choice of ancestors," tuts a snob. If he wants to earn medals, those shiny bits of bronze and silver that have gotten men killed for centuries, he'll have to sail to South America to map, or really referee, the rubber-rich border between Bolivia and Brazil.

With sidekick Henry (Robert Pattinson, happily hiding in Teddy Roosevelt cosplay) and a copy of Rudyard Kipling's “The Explorer,” the bushwhacking explorer spends years hiking, rafting, starving, and ducking deadly arrows. His men vomit black blood. Several die (one in, yes, a piranha attack). But Fawcett becomes addicted to the danger, especially his dream of discovering the ruins of Z, a gold-plated jungleopolis gobbled up by the trees.

The real-life man was one of a generation of explorers whose adventures inspired Indiana Jones. Fawcett was more himself in the wild than society let him be in London. He spent his life fighting to get to the Amazon and then fighting his way out, funding some of his trips with his own fame by selling dispatches to newspapers in America, where millions of readers relished his battles with maggots. When he’s forced to pause for World War I, he kisses a pencil sketch of a palm tree in the trenches. The forest, not his family, gives him strength. Fawcett’s friends call him obsessive, crazy, cocky, reckless. But Hunnam, unlike that mad movie conquistador Klaus Kinski, needs more insanity in his eyes. Hunnam plays Fawcett at a hum, except for one scene in which he heckles the Royal Geographical Society into sponsoring his next quest. He's so calm that the character almost full-circles into being serial killer–esque (and he does murder Nina's wish for a contented home).

Decade after decade, Fawcett returns to risk near-death — and certain resentment from the growing family he leaves behind. After all, South America was a long steamer away from England, and his return, if possible, is open-ended. (Eventually, he won't return.) There's a lovely sequence in which Fawcett rides a rural train that the camera imagines chugging past his sleeping children, one of whom grows up to be played by new Spider-Man Tom Holland. It's the literal passage of time. Still, the script, adapted by Gray from New Yorker journalist David Grann's best seller of the same name, seems to have lit its calendars on fire. Two-year trips seem to take two weeks, and even its head count of Fawcett's men is haphazard. After several desperate river scenes in which Fawcett appears to be stuck on a raft with a stripped-down quartet, he expels a sick man (Angus Macfadyen) with two never-before-seen guides and the group's last horse. Horses? In what backpack did he stash those?

Despite Fawcett's agonies, Miller's Nina, walled-off in yet another wifey role, wants to join the plot. We, too, get grouchy that she keeps getting ditched for mosquitos. When her modern-minded mother of three boasts that she's learned to navigate by the stars, we're expecting her to strip off her corset and shimmy into capris. Just what the jungle needs! Another babe with moxie. But to its credit, The Lost City of Z isn't that kind of movie. Gray, who specializes in small, serious dramas, refuses to hit a phony note. He resists buffing Fawcett's biography into a glossy action flick. Instead, he erases the triumph and the visual splendor from Fawcett's story. What's left underneath is all smudged and somber. The mist hangs. The narrow escapes are depressing. Even the trees look sad.

The Lost City of Z is so jarringly out of step with summer blockbuster season that watching it feels like discovering a relic. Today, any film about a colonialist confronting remote tribes must be run through the 2017 political filter and judged on philosophies its primitive white characters had yet to discover. Take last year's The Legend of Tarzan, which dodged its blond-hero problem by letting African crocodiles save the day. Alexander Skarsgård's Lord Greystoke cooled his feet in the water and cheered. But Gray reaches past the adventure serials of the 1920s, even beyond Tarzan himself, whom Edgar Rice Burroughs invented after Fawcett emerged from the forest.

Fawcett finished his quest before movies had the technology to make us hear Tarzan yell. His legend predates the look and sound of the films we’d make about men like him, hijinks-prone fictional ancestors who’ve shaped adventure movies for the next century and counting. The man himself has almost never been put onscreen. Which gives Gray the freedom to introduce him as a proto-progressive who wanted to find Z to prove that Europeans didn't patent civilization, a hot take that makes Fawcett's fellow Brits howl as if he's announced that cats were the first species to fly to the moon. In reality, he also theorized Z might have been founded by gringos from Atlantis.

Compared to his contemporaries, Fawcett was relatively open-minded. He at least saw the local Bolivians as humans. Still, he's content to use slaves, even though Hunnam shows him shuddering at the whip scars across his guide's back. Applauding him for being kinder than most colonizers is like being grateful that chicken pox isn't Ebola. The natives continued to suspect — correctly — that the white man meant death, and the white men feared the same of them. History, including living history being made in Syria and Sudan, rarely shows two cultures in harmony. Humanity remains savage.

The Lost City of Z doesn't dirty its hands "solving" racism. It has its own impossible ambition: to sell an au naturel jungle drama on the same week Vin Diesel outraces a submarine. Gray steers his film in the opposite direction. Instead of a thrilling climax, he chooses to let the story evaporate into the Amazon fog. Yet this odd film left a chill in my bones that I'll be thinking about all summer. I keep coming back to a moment when Fawcett's party encounters a tribe of cannibals. Lunch is roasted man on a spit. Fawcett doesn't attack the tribe's morality, or grandstand about his own purity. He simply insists, "We must attempt to engage." That should be the mantra of all explorers, whether in the wild or at the movies.