Toward the beginning of the new film The Green Knight, King Arthur turns to Gawain, his young nephew and (later) one of the most famous Knights of the Round Table, and asks him to tell a story. Ashamed, Gawain (played by Dev Patel) tells Arthur (Sean Harris) that he has no stories to tell. Arthur’s wife, Queen Guinevere (Kate Dickie), smiles and says, “Yet.” Viewers immediately know that adventure awaits—a feeling confirmed soon after, when the mysterious Green Knight appears at the court’s Christmas celebrations. Gawain accepts the Green Knight’s challenge of a “Christmas game,” setting the stage for a saga filled with magic, horror and—ultimately—honor.

Written, directed and produced by filmmaker David Lowery, the movie is based on a 14th-century Middle English poem titled Sir Gawain and the Green Knight. Some of the details between the film and its source material are, of course, different, but the themes at their respective hearts remain consistent. In both, Gawain launches on a journey that is as much about self-discovery and contemplation as it is about an epic, heroic quest to vanquish a magical foe. In fact, much of the poem is about how Gawain is readying to face his doom, waiting for the Green Knight to repay the blow that Gawain struck the Christmas before.

Although the poem only exists in one manuscript copy, it’s been celebrated in both popular and academic culture for the past several centuries. Richard Godden, a literary scholar at Louisiana State University, explains how the medieval poem subverts readers’ expectations: People tend to think that “medieval literature didn’t have a sense of subjectivity and self-consciousness,” that people living in the European Middle Ages didn’t think about themselves and their place in the world. But that’s just not true. Sir Gawain and the Green Knight “is a kind of coming-of-age story,” says Godden. It’s all about Gawain becoming a man, about Gawain becoming “Gawain.” In the film, rendering Gawain as younger, as yet unaccomplished, and not really even a knight, a man who over the course of the movie has to confront difficult situations on his own, makes the medieval theme of “becoming”—of growing up—all the starker.

The original 14th-century source is set in what one can think of as the “Arthurverse,” a broad and loosely connected collection of stories centered on Arthur and produced over the course of several hundred years. Unlike modern franchise universes, no one had authority over the stories of King Arthur and his court; rather, Camelot was just a convenient setting with familiar characters whom medieval writers could feature in any kind of story they wanted to. Gawain shows up in many of these tales, usually as one of Arthur’s most heroic, perfect knights.

Not so in the film. We first meet Gawain in a brothel, where he begs his lover to stay in bed rather than go to Christmas mass. We learn that he’s Arthur’s nephew, the son of the king’s sister (played by Sarita Choudhury), whose witchcraft—perhaps in cahoots with Arthur—sparks the drama. At the Christmas feast, a Green Knight, a massive creature of wood and moss, strides into the hall and challenges the knights to trade blows with him. His opponent will strike their blow now, while the Green Knight will take his at the Green Chapel on Christmas one year later. Gawain lops off the knight’s head. But the towering figures picks his head right back up and rides off after uttering the ominous warning “One year hence.”

Afraid and unsure after a stressful year of waiting, Gawain rides out to meet his fate. What follows is a strange, episodic journey: being robbed, recovering the head of a decapitated saint, speaking to giants, meeting a mystical fox, freezing in intense cold, staying with an odd group of nobles who seem to know more than they say. Throughout the quest, viewers watch Gawain ask overarching questions about what it means to become an adult, as well as more specific queries like what to do when you want to have sex with the wrong person.