“I want to talk about America, and I want to tell you why I wrestle,” says a very awkward Mark Schultz (Channing Tatum) to a class of bored, bemused but polite primary schoolers, in Foxcatcher (in national release), Bennett Miller’s largely compelling dramatisation of a strange true story. The real Schultz won gold in wrestling at the 1984 Olympic Games in Los Angeles. In the film’s opening scenes, we see that after this triumph he lives alone in a nondescript flat, that wrestling is his life, and that for his speaking engagement he’s paid $20.

At a wrestling gym he spars with his older brother, Dave (Mark Ruffalo), and it gets rough, fast. (The real Dave Schultz also won gold at Los Angeles, and was a wrestling coach of note.) Dave has a growing family and seems balanced. Mark is more of a brooder, nursing secret wounds that we can hardly see for all that muscle. He loves his brother, but would like to step out from his shadow.

The square-jawed Tatum plays “dumb” readily. He can do it with comic ease, as in his dumb-cop partnership with Jonah Hill in 21 Jump Street (2012) and its sequel, and he can be more nuanced, as in Steven Soderbergh’s Magic Mike (2012), where he is a simple male stripper with a belief in the wondrous possibilities of capitalism. As Mark Schultz, he’s not so much dumb as compact, guarded – conserving all his animal energy so there’s not much left for analytics.

One evening, Mark gets a phone call from someone calling on behalf of John E du Pont – “of the du Pont family”. The name means nothing to Mark, but the caller tells him Mr du Pont would like to fly Mark to visit him – “first class, of course”. Intrigued, Mark goes to Philadelphia, where he’s taken by helicopter to Foxcatcher Farm, the du Pont family property in rural Pennsylvania. (DuPont, a multibillion-dollar family company founded in 1799, was the largest supplier of military explosives for the US in World War One, and later created nylon, Teflon, kevlar and lycra.)

Foxcatcher Farm is an impressive spread: stables, a labyrinthine mansion, trophy rooms. “Do you have any idea why I asked you to come here today?” asks du Pont (Steve Carell). “Do you have any idea who I am?”

“No, sir. No,” replies Mark.

“Well, I’m a wrestling coach, and I have a deep love of the sport of wrestling. And I wanted to speak with you about your future.” Du Pont asks if Mark feels he’s getting the support he needs. “You know how the Soviets support their wrestlers.” “I do,” says Mark.

“We as a nation failed to honour you,” says du Pont, “and that’s a problem not just for you, but for our nation.” It’s the “failed to honour” that strikes a chord with Mark – those $20 cheques, some possible moment of glory every four years … and for what? “I’m a patriot,” says du Pont. “And I want to see this country soar again.”

If he’s a patriot, it’s only in service to his narcissism. Something is not quite right with him. He’s a loner, too, but with the money to service his weirdest, wildest quirks. His mother (played with steely disdain by Vanessa Redgrave) thinks wrestling is a “low sport” and values her horses more than anything; much of du Pont’s energy is spent trying to win her favour, or at least prove to her that he is a man. His dream is to use the family estate as a live-in training facility for the American wrestling team as it prepares for the Seoul Olympics in 1988. When du Pont asks Mark what he wants, you know he already knows the answer: Mark wants to be the best in the world, and to win gold at the upcoming “Worlds” and at Seoul. Du Pont has the perfect lure – such a gleaming new facility! – with which to reel him in.

At first, Mark sees du Pont as an eccentric benefactor who can be harnessed to suit his own needs. But things gradually become muddier than that, and the film charts the cloying, unhealthy relationship between the eccentric industrialist with a mother complex and the sullen wrestler with a brother complex.

Mark installs himself at Foxcatcher Farm. Dave, with his wife and kids in Pittsburgh, doesn’t. In the early sequences, the melancholy soundtrack and muted colour palette bring to mind the dreary, small-town, down-and-out Pennsylvania so poignantly rendered in Michael Cimino’s study of a lost generation, The Deer Hunter (1978). For Mark, after the rain-soaked streets and the clapped-out car, the du Pont estate is a blaze of patrician lushness. There’s just the small problem of crazy John. “I consider us friends,” du Pont tells Mark. “And most of my friends will call me Eagle. Or Golden Eagle. Either will work.” Mark ponders this mutely. “Or John,” adds du Pont, weakly – yoking bathos to pathos in a way that’s both heart-rending and pitiful.

Miller wrote and directed Capote (2005) and Moneyball (2011), character studies that evince great depth. In Capote, Philip Seymour Hoffman’s Truman Capote knows exactly the prize he’s after: he wants to create a new kind of nonfiction, a book – In Cold Blood – that will ring down the decades. In Moneyball, Brad Pitt, as baseball manager Billy Beane, has to learn how to adapt to statistics nerd Jonah Hill’s new methods of player analysis. Capote and Beane are sharp and driven, and for all their insecurities have a sense of who they are. In Foxcatcher, Miller enters new territory: his John du Pont is a compelling portrait of delusion and pain, a mesmerising grotesque whose sheer wrongheadedness makes much of the film a wicked pleasure.

Mark, alone in his accommodation, not allowed into the main house, grows anxious that he might let du Pont down. They become entwined, co-dependent. There’s a distant hint of the homoerotic, when du Pont grapples – pathetically, ineptly – with Mark, trying to “demonstrate” to him his own wrestling moves. They drink, they do cocaine. The rest of the wrestling team arrive, and in the end Dave comes too. No one respects du Pont, who has anointed himself team leader. They’re happy to take his money and use his facilities and shoot glances at one another, even when his behaviour is off the deep end. “Three hundred and eighty-seven days to Seoul, gentlemen,” says du Pont, walking into team practice and firing his gun into the ceiling. “Let’s have a good practice, shall we?”

Dave sets out to “reclaim” Mark, who has been binge eating, is nowhere near peak fitness, and is 12 kilograms overweight for the upcoming selection rounds. In the usual Hollywood fare, we’d have a saccharine reunion, and family love would win out. Miller is more considered than that: the film in a sense charts Mark’s slow journey out of bewilderment, towards a rudimentary sense of self, but the vehicle of its forward momentum is a gravely ill du Pont, who would treat Mark as his prize puppy and his chance at being recognised by his mother and by the world.

“Mother, I am leading men,” he informs her at one stage. She looks as if she knows better, but nonetheless one day deigns to visit a team practice. When du Pont sees his mother at the back of the gym, his entire demeanour changes: he attempts to give an inspirational speech to the team, but it’s like he’s a little child putting on a show. It’s excruciating – hard to watch, hard to look away – and one of the best scenes in the film.

Carell is a marvel. The film led me to watch YouTube clips of the real John du Pont, grandiose, scattered and self-promoting, back in the days before the events depicted in Foxcatcher cut his freedom short. Carell has played buffoons well, from his mentally challenged weatherman in the silly but enjoyable Anchorman films, to Michael Scott in the American version of The Office. As John du Pont he gives us a glimpse of how good a serious actor he might be. We have seen buffoons before, but never one with such creepy, skin-crawling menace.

The worst of him is the ruthlessness with which he cannibalises Mark’s innocence. Early, du Pont parades his protégé at a gala fundraising event that we come to realise he has created in his own honour. There, he manipulates Mark into reading a prepared speech. Later, we see how the speech gets incorporated into a slick video further promoting du Pont’s greatness. “I spent my lifetime looking for a father,” reads Mark out loud, stiltedly, “and I found one in the Golden Eagle of America, John du Pont.” It’s then we realise just how much Miller has created, buried beneath a luridly fascinating biopic, a tale of Gothic horror.