In 18th‑century France, Lia de Beaumont, a loyal servant of Versailles and King Louis XV, is found dead in the Seine. She lies in a coffin marked with the word “Psalms,” her body preserved by mercury poisoning to prevent decay. According to the Church, a soul bound to a corpse that cannot be buried in the earth will forever wander the human realm, barred from Heaven. This conviction deeply affects her brother, D’Eon de Beaumont, a spy for the king, who vows to discover who murdered Lia and why. Yet he never expected that the agent of revenge would be Lia herself, now inhabiting D’Eon’s body. The quest could jeopardize France.