1873. At an abandoned ch'teau on the outskirts of Paris, a dark séance is about to take place, led by acclaimed spiritualist Vaudeline D'Allaire. Known worldwide for her talent in conjuring the spirits of murder victims to ascertain the identities of the people who killed them, she is highly sought after by widows and investigators alike. Lenna Wickes has come to Paris to find answers about her sister's death, but to do so, she must embrace the unknown and overcome her own logic-driven bias against the occult. When Vaudeline is beckoned to England to solve a high-profile murder, Lenna accompanies her as an understudy. But as the women team up with the powerful men of London's exclusive Séance Society to solve the mystery, they begin to suspect that they are not merely out to solve a crime, but perhaps entangled in one themselves.