Beatrice Portinari is Dante Alighieri's fiancée, a Crusader. Before Dante leaves for the Third Crusade, they consummate their union; she gifts him her cross as a token and implores him to protect her brother Francesco during the war while forsaking "all pleasures of the flesh" for her sake. Secretly, Beatrice strikes a Faustian pact with Lucifer: Dante's fidelity guarantees his safe return, but his adultery forfeits her soul to Hell, making her Lucifer's bride.

In the Crusades, Dante sleeps with a Muslim slave girl who trades "comfort" for freedom for herself and her companion—later revealed as her husband. This infidelity voids Beatrice's pact. Roughly three years later, the slave girl's husband, the Avenger, attacks Dante's Florentine home. Alighiero, Dante's father, dies in the assault. Beatrice suffers a fatal stab wound while fleeing and perishes moments before Dante arrives. Lucifer claims her soul instantly per their agreement.

Within Hell, Beatrice initially manifests as a translucent, ghostly figure with radiant skin, a bluish aura, and visible venous lines. She beseeches Virgil to guide Dante through Hell to save her, vowing to praise Virgil to God upon her salvation. At the river Acheron, Beatrice briefly confronts Dante, questioning his broken vow. Deeper in Hell, her appearance shifts: in the Circle of Lust, she dons a monstrous, form-fitting gown of demonic flesh adorned with spikes and a jagged collar; her hair coils into horn-like structures. Lucifer reveals Dante's infidelity here, forcing her to witness the memory through Dante's eyes.

Her corruption deepens in the Circle of Anger. Lucifer taunts Dante about his betrayal and offers Beatrice a pomegranate that transforms into three seeds. Ignoring Dante's pleas, she consumes them, undergoing an agonizing metamorphosis into a demonic entity. Her skin pales and burns; her arms blacken into fiery claws; horns supplant her hair. A gown of writhing damned souls envelops her, and she towers over Dante. As Lucifer's consort and Queen of Hell, she kisses him passionately before they depart.

In the Circle of Fraud, Beatrice arrives antagonistically on a bone litter borne by demons. She denounces Dante as a fraud and summons the demon Malacoda to slay him. Following Malacoda's defeat, she compels Dante to traverse the ten ditches of the Malebolge, unleashing minions against him while contemptuously declaring he belongs among the damned. After he completes the trials, she confronts him about his betrayal and his role in her brother Francesco's death. Dante relinquishes hope, placing her cross on the ground. This act purges Lucifer's influence, restoring her ethereal form. She thanks Dante, forgives him, and is borne to Heaven by the archangel Gabriel, who promises their reunion.

After Dante defeats Lucifer, a vision shows Beatrice and Dante in Purgatory, naked yet partially obscured by mist. They clasp hands before she vanishes, returning to await his eventual arrival as promised.