After the debacle that was the final season of Game of Thrones, it’s probably a good idea to go back to the origins of the sword-and-sorcery genre. What is it about medieval knights and monsters that resonates with people centuries later? There have obviously been plenty of attempts at the Arthurian legend; Hollywood tends to like it when a story has no rights or licensing to negotiate. But what about a tale from a later period in the “history” of Camelot?

That’s exactly what we have in the epic poem known as “Sir Gawain and the Green Knight”, first recorded by an anonymous scribe in the 14th century, but which may be quite a bit older. As a classic tale of chivalry, most stories about brave knights defending their kingdoms and achieving honour for themselves lead back to the poem. It’s no coincidence that one of the most popular translations from the original Middle English was by J.R.R. Tolkien.

Screen adaptations of the poem have been few and far between - perhaps it’s too easy for screenwriters to focus on familiar King Arthur instead, and just figure out whether to present him as a Roman soldier or as a medieval version of The Flash. That’s a shame, because the Gawain story is packed with powerful themes and symbols, just waiting for the right filmmaker to lay them out.

David Lowery is just that filmmaker. Following his last film, the more contemporary The Old Man and the Gun, Lowery returns to the elegiac tone he used in his remarkable 2016 film A Ghost Story, unspooling Gawain’s quest with exactly the kind of patience and striking imagery that the tale deserves. Sir Gawain and the Green Knight is not a story of massive battles or overwhelming magical events; it’s considerably more psychological and intimate, and Lowery’s The Green Knight fittingly creeps into your mind and takes root.

Gawain (Dev Patel) is the youngest member of the Knights of the Round Table. He’s Arthur’s nephew, and the son of the witch Morgan le Fay (Sarita Choudhury), but has yet to achieve the kind of deeds that would make him feel like he’s earned his place at court. One Christmas, an unexpected opportunity presents itself. A gigantic knight clad in green rides into the castle, proposing a game: he will allow any knight to strike him once, provided they meet him one year later to receive the same blow in return.

Sensing that this might be his chance to prove himself, Gawain beheads the knight, only for the knight to stand up, collect his head, and ride away laughing. Now it’s Gawain’s duty to travel to what he assumes will be his death, in order to honour his kingdom and himself. Along the way, Gawain’s dedication is repeatedly tested, forcing him to question whether honour alone is worth dying for, and whether there are ways to escape his fate.

The Green Knight is undoubtedly a slow-moving film. The camera sweeps over Gawain as he traverses the misty, almost post-apocalyptic landscape. There are frequent suggestions of bloody battles happening around him, though we don’t see them on screen. In a beautiful sequence, Gawain encounters a group of female giants, who appear to be leaving Gawain’s world forever. It’s as though Gawain is always too late for the action, and that he’s running out of time to become a real knight before the world forgets about chivalry and epic quests.

Many scholars have studied the themes of the story over the centuries, but the starkest one that emerges during the first viewing of Lowery’s film is the danger of claiming status and riches through dishonourable deeds. Several characters try to offer Gawain an “out” from his obligation, and given what he knows he must give to the Green Knight, he’s hard-pressed to turn down these offerings. Yet he pushes forward, and Patel’s performance anchors these scenes; you can track his eyes frantically bouncing between his options. Given the same choice, would you make the same call?

Lowery submits to a few indulgences himself: the film uses a number of ornately scripted intertitles, like pages from an illuminated manuscript, which might feel haughty to some viewers. But the production is otherwise impeccable: a haunting soundtrack by Daniel Hart, cinematography by Andrew Droz Palermo that burned into my brain, and muted costumes that evoke a kingdom in decline, in need of fresh blood. After the mad rush of the final episodes of Thrones, cramming plot down our throats, it’s refreshing to have some room to breathe and understand a character’s motivations.

The rest of the cast is also well-chosen. Alicia Vikander does double duty as two women connected to Gawain, and Joel Edgerton appears as a mysterious lord who offers Gawain hospitality. Sean Harris gives us a fading Arthur who’s past his prime, and Barry Keoghan once again burrows under your skin as a distinctly off-putting scavenger.

As much as I enjoyed The Green Knight, I can’t put it forward as a universal recommendation. You need to have a certain familiarity with old-school sword-and-sorcery, or classic literature in general, to get the most out of it. But if recent versions of this world - like the recently-cancelled YA series Cursed on Netflix - left you cold, The Green Knight is exactly the thing to warm you up.

The Green Knight gets four stars out of four.

Stray thoughts

• I really need someone to write the definitive analysis of the indelible quality that unifies A24 movies like this.

• The encounters with Winifred (Erin Kellyman) and with the giants gave me big flashbacks to the Hellboy comic books.

• This movie is already my favourite for the production design category at the Oscars next year.