Plot
Anne and her mother-in-law, Morwen, late-medieval peasants, scrape by while awaiting Seamus’s return from the Wars of the Roses. Introspective, sweet, and devout, Anne contrasts with Morwen, a crude grifter bent on survival. Despite this, they are devoted to each other.
Jago, Seamus’s childhood friend, returns from war claiming they deserted but Seamus was killed by thieves. Morwen doubts him, but his tale confirms Anne’s dream of Seamus’s death. Anne begins glimpsing an armored knight in the woods.
Jago courts Anne, while Morwen warns that he has always envied Seamus and will steal her away, frightening Anne with threats that the Knights of Hell will drag the girl to Hell if she abandons her duty towards Morwen and forgets her late husband. When a ship wrecks nearby, the women scavenge it; Morwen secretly kills survivors. She later slits the throat of a pilgrim priest, Friar Penrose, for his relics, and a horrified Anne helps hide the body.
Anne grows closer to Jago, who comforts her that the knight she has continued to see is likely a real person. After dreaming of Morwen as a demon, sleeps with him. He urges her to leave Morwen and live with him, but Anne confesses that Morwen both needs and frightens her. Morwen tightens her hold, using Anne as a distraction to kill and rob a traveler. A horse figurine from one victim seems to Anne a sign from the demonic knight.
Morwen threatens Jago with a knife when he comes to the cottage to see Anne, and terrifies Anne with tales of the Knights of Hell should she leave. After an internal spiritual struggle, Anne drugs Morwen and sneaks away to spend a joyful day with Jago. When Morwen wakes, she encounters the knight herself and follows him to the lovers. When the knight collapses, clawing at his helmet, she kills him for his purse.
After their night together, Anne confides her envy of the local Lady’s wealth and her fears the demon Mammon has been influencing her to Jago, who assures her such feelings are natural. Anne resolves to live with Jago, defying Morwen, who reacts poorly. The couple's new life quickly sours when Anne catches Jago in a lie about how Seamus died. Jago confesses that the truth is that Seamus had grown ruthless and frightening in war, murdering comrades for loot. He killed an armored knight and stole his helmet; upon wearing it, screamed as if burning. Jago fled and later lied about Seamus’s death to win Anne.
In a flashback, Morwen removes the dead knight’s helmet and discovers she killed her own son, his face grotesquely diseased and demonic. She dons the helmet to frighten Anne, but it burns her and she cannot take it back off. Anne splits the helmet with a cross, revealing a now-disfigured Morwen covered in boils and pustules, begging forgiveness for her sins.
The cursed helmet restores itself. Anne, unafraid, picks it up despite Morwen’s warnings and appears like an angel to Morwen before the woman goes blind. Rejecting both Jago and Morwen’s claims of ownership over her, Anne retrieves the helmet from a chest in the woods, and listens as it whispers to her.
