In the aftermath of World War I, a new kind of horror emerges in 1920s America as monstrous demons, embodiments of sin, begin to plague the land. The Order of Magdalene, a holy organization under the Council of the Catholic Church, steps in to combat this threat. Sister Rosette Christopher, a daring young member of the New York branch, joins forces with the demon hunter Chrno, armed with holy weapons but often causing collateral damage in their missions. While their actions may not sit well with Sister Kate Valentine, the branch leader, Rosette is supported by Father Ewan Remington and weapon developer Edward Hamilton. Chrno, with a mysterious past and a deep connection to Rosette, adds a layer of complexity to their partnership. As they face increasing demonic incursions and search for the source of the upheaval, Rosette also pursues her personal quest to find her missing brother, Joshua, forging a bond of trust and reliance with Chrno in their dangerous battles.