The first episode is a masterclass in building dread from a single image: a sister's poisoned corpse in a coffin, and a brother who can't let her go. D'Eon becomes a spy possessed by something between grief and duty, caught between the Church's certainty that his sister's soul is trapped and his own need to believe he can still save her. The animation from Production I.G. gives every frame, every candle, every silk thread, every moment of swordplay, the weight of genuine consequence, making 18th century Versailles feel like a place where the supernatural actually lives. The middle drags under its own mythology, but the visual precision and emotional core never waver: this is a show about a man refusing to let his sister's death mean nothing, no matter what it costs.

In 18th century France, D'Eon de Beaumont serves King Louis XV as a skilled spy. Everything changes when his sister Lia surfaces in the Seine, her body preserved in a coffin marked with the word "Psalms." Mercury poisoning has kept her corpse from decaying, and by the Church's teaching her soul is now doomed to wander the earth. D'Eon swears to uncover who murdered her and why, and his search for the killers leads him to the secret police and a string of disappearances across Paris. His investigation takes a supernatural turn when Lia's vengeful spirit possesses his body. Clues point to a conspiracy among French and Russian nobles, urged on by a cult, while a mysterious group called the Rose Cross stands in his way, using dark powers to create a creature called the Gargoyle in a bid to take over Europe. This mystery with supernatural elements retells history through a tale of vengeance, loyalty and betrayal.