Depending on whom you ask, The Lost City of Z, the new movie from American independent filmmaker James Gray, is many things: a straightforward Amazonian adventure story about the early 20th-century British explorer Percy Fawcett, a throwback to the classical American cinema of yesteryear, a work of historical revisionism that erases its protagonist’s reputation as a racist and eugenicist, a quietly autobiographical film about its director’s own search for the sublime, a transcendent work of fine art, a colossal bore. All or none of these may be true, though if you ask me, Lost City is above all else a cautionary tale in how to ruin what might otherwise have been a masterpiece.

Lost City begins auspiciously enough, with a rousing scene of British equestrians hunting game while bagpipes blare earnestly in the background. From there we proceed in short order to the ballrooms and drawing rooms of the aristocracy, where ballroom dancers, corset jokes, and impeccable facial hair abound. Our hero, Fawcett (Charlie Hunnam), does not belong in this world; despite his excellent shot, we learn from the snide remark of one of his superiors that Fawcett has been “rather unfortunate in his choice of ancestors,” namely an outcast, drunkard, dead father. Nevertheless Fawcett is a promising enough talent to catch the attention of London’s Royal Geographical Society, which enlists him to travel across the Atlantic for a charting mission in the wilds of Bolivia.

Fawcett arrives in the Southern Hemisphere on cue with a “Rite of Spring” needle drop, but after not more than 30 minutes’ exploration and adventure, Fawcett returns, unexpectedly, to Great Britain. The historical Fawcett made seven trips back to the Amazon in his lifetime to attempt to prove the existence therein of a technologically advanced civilization (much to the consternation of an incredulous scientific establishment) before vanishing on his final mission in 1925. Lost City condenses the timeline to show us only three visits, along with the interstitial periods of his life spent in Europe raising a family with wife Nina (Sienna Miller, doomed, it would seem, to always be cast as the sidelined wife) and fighting in the trenches of the Great War. Gray switches from one venue to the next gracefully; anyone complaining that the film deviates from the standard narrative progression into the heart of darkness we’ve come to expect from Joseph Conrad’s novella and its thematic offspring is missing the point and, for that matter, the real problem besetting this movie.

Gray is setting us up for a grand narrative of exploration and obsession, and Hunnam is not the right actor for the job. Fawcett, at least as Gray’s screenplay depicts him, is a cocksure man gradually lured into the enigma of the jungle and the promise of discovery. The movie would have benefited from an actor who could intuit Fawcett’s idiosyncratic psychology and outsider status and project them with imperceptible effort, before any expository lines of dialogue are placed in his mouth. The Fawcett we get bears more of a resemblance to those loud, generically handsome, progressively minded, and well-intentioned men you find on every street corner and in every Logan Circle happy hour in Washington, D.C. Never mind that the rest of Lost City’s British male ensemble are suitably stodgy: this is not the anachronistic contrast you want to strike.

Hunnam was not Gray’s initial choice for the part of Fawcett—Brad Pitt and Benedict Cumberbatch’s names are attached to the film’s production lore—and one almost wishes Gray hadn’t settled for good enough, given that Hunnam’s misbegotten casting serves a film that’s so technically magnificent. Gray somewhat miraculously shot his entire movie on 35mm film—a challenge in the digitally dominated filmmaking landscape of 2017 to say nothing of the Amazon—to the benefit of all who have eyes to see. Cinematographer Darius Khondji renders all of the movie’s surfaces with a soft texture that lends a mythic quality to the jungle scenes at the same time that it gives tangibility to the vintage fabrics of the cast’s wardrobe. The film is at its best not when Hunnam is derogating the close-minded assembly of the Royal Geographic Society with oratorical insipidity so much as when it hushes him up and lets the evocative alchemy of light and fog and wood and fire—in the depths of the rainforest or in the close-drawn quarters of a Fawcett’s Devonshire domicile—speak for themselves.

In the visually and aurally spectacular final 15 minutes or so of the film, I was caught off guard by the sudden stirring in my soul of theretofore unfelt emotions for the movie’s human characters. Where did these come from? Why, for the first time in the past two hours, am I now invested in the fate of the Fawcetts? Maybe it’s the old-age makeup stiffening Hunnam’s otherwise unbridled maw in this last act, or maybe it’s the fact that Hunnam moves to the back and disappears from the screen while Miller and Tom Holland, the latter playing Fawcett’s eldest son and final traveling companion, come to the fore and disappear into their roles. Their performances are so believable and unpretentious that they throw a much harsher light on the miscasting of Lost City’s lead actor.

It’s a shame that Hunnam is so unfit a cornerstone for Gray’s project. A cathedral’s towering spires and intricate arches may be magnificent on their own, but a neglected foundation renders the whole building architecturally unstable.

Tim Markatos is editorial fellow at The American Conservative.