Lia de Beaumont is the elder sister of D'Eon de Beaumont, the protagonist of Le Chevalier D'Eon. In life, she was a noblewoman who served King Louis XV of France as a spy and diplomat, and she was widely regarded as one of the finest swordsmen in the kingdom. She also served as an instructor to the dauphin, Auguste, and was a close friend and teacher to Anna. A student of the swordsman Teillagory, Lia possessed a natural talent for poetry and was beloved by nobles and royalty alike, including Empress Elizaveta of Russia, who held her in high esteem. Despite her gentle and considerate demeanor in life, her untimely death under mysterious circumstances transformed her into a vengeful spirit. Her body was discovered floating in a coffin on the Seine, with the word Psalms written in blood on the lid. Driven by profound anger, sorrow, and a burning desire for revenge, her restless soul takes possession of her younger brother D'Eon, manifesting through him to exact vengeance on those who wronged her. Throughout the story, Lia's spirit acts as a driving force, guiding D'Eon as he investigates the truth behind her murder and the dark conspiracy involving a cult, the French and Russian nobility, and the disappearance of women. Her presence is also marked by a unique sword stance that her former teacher Teillagory recognizes, confirming her identity when others are uncertain. As the narrative unfolds, it becomes clearer that Lia had deeper connections to figures such as Maximilien Robespierre and others in the royal court, and her past is gradually revealed, showing that she was not as innocent as she initially appeared. Her ghostly influence compels D'Eon forward, and her abilities as a peerless fencer and a skilled agent of the crown are crucial to the plot. Her role is thus that of both a catalyst and a constant supernatural presence, whose unresolved anger and yearning for justice shape the entire story.