Forget the bombast of Indiana Jones movies, this is a sedate trek through the Amazonian jungle, with Sons of Anarchy star Charlie Hunnam severely clipping his accent to play real-life British explorer Percy Fawcett. 

In the early 1900s, he led a series of expeditions aiming to find evidence of an ancient civilisation, a journey bristling with intrigue and as much frustration.

Although noble in the pursuit of knowledge, Fawcett is hampered by aloofness and calmly accepts the rift that grows between him and his young family whenever he disappears for years at a time. Benedict Cumberbatch was originally slated to play the lead, and he might have brought more of an edge to Fawcett, for whom sacrifice gradually becomes a destructive fixation, whereas Hunnam plays him with a bland kind of fortitude.

Robert Pattinson adds colour as his right-hand man, Henry Costin, bearded and bespectacled, always looking as though he’s trying to shake off a hangover – far from the teen idol who set pulses racing in the Twilight movies. The pair's mission, as outlined by the Royal Geographical Society, is to map the border between Bolivia and Brazil, where local conflict threatens British interests in the area (namely, rubber plantations). But Fawcett wishes to return because of evidence he finds (carvings and fragments of pottery) that support local tales of a lost civilisation.

Many at the RGS won’t entertain the idea of “savages” being elevated above their station or lend credence to the myth of El Dorado, but Fawcett has just enough support to make repeated trips, each one thrown off course by hostile tribes, disease and growing weariness. The air feels thick with danger, humidity and pestilence, and a scene where the men are entertained by cannibals is particularly striking – the remains of dinner still smouldering above a fire. Just as halting is Fawcett’s measured response to this, putting the quest for knowledge above all sensitivities.

Meanwhile, Sienna Miller swallows a lot of resentment as his wife, who believes wholeheartedly in what her husband is trying to do, despite the ridicule heaped upon him. She brings much-needed heart to an otherwise matter-of-fact account of Fawcett’s life. There is fire, too, in the belly of their eldest son (Tom Holland) who has an obvious abandonment complex. Fawcett gets off lightly, however, with bonds only mildly tested and loved ones generally acquiescing to his righteous justifications about the way humanity will benefit from uncovering the “City of Z”.

It’s only when Fawcett’s staunchest ally, Costin, expresses some doubts about their continued efforts to find Z that some tension is injected into the often loose and rambling plot. The seeds of his discontent aren’t sown early enough, though, making it something of a lost opportunity to present Fawcett as others saw him – not necessarily noble, perhaps even crazed. After all, his first trip is motivated by a need to elevate his family’s social standing, and too often the lives of his men are put at risk.

It's biologist and Antarctic explorer James Murray (Angus MacFadyen) who's made the villain of the piece, initially for failing to keep pace and then for being accused of stealing rations. But it’s hardly a rounded portrayal – only one step from moustache-twiddling evil. 

Writer/director James Gray (We Own the Night) delivers a very subdued film overall, right down to the washed-out visuals, but the doggedness of Fawcett sparks a sort of morbid fascination with how far he is willing to go to prove his theory. An increasing sense of impending disaster looms, but, when the moment finally arrives, Gray swerves the chance to have Fawcett finally look himself in the mirror and ask, "What was it all for?"

Of course, Fawcett would be vindicated after his death with various discoveries made to prove the existence of an advanced civilisation, but here the more tantalising question – that drags you along yet is left unanswered – concerns the psychological make-up of this unique individual.

The Lost City of Z is in cinemas Friday 24 March


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