The worn-out portraits of a once-happy family now collect dust in their vacant, cursed home. Horror surrounds the abandoned mansion, in which a sick wife murdered her husband. The household's children—Lillian Helena and William "Will" Grant—were adopted separately. While Will joined the house of family friend Marquis Alexander Daniel Leondin, Lillian moved in with the Clearwaters. Despite her new family raising her as one of their own, Lillian never felt like a true Clearwater. When Lillian's adoptive father passes away, her mother sends her to the Recksell Brookside Mansion, where Will now rules as the marquis. Lillian's new home is comfortable, and her brother makes their reunion more special than she ever thought it would be. But terrifying nightmares haunt Lillian, strange shadows disappear behind the corners, and the servants unnervingly hide something from her. Emerging bizarre feelings daunt Lillian, and while Will too conveniently has a rational explanation for everything, Lillian begins to doubt that anything around her is as it seems. [Written by MAL Rewrite]

19th End Century Memorandum is an adaptation of Bu-kyeong Cho's 19 Segi Bimangnok web novel series. It is originally a webtoon series which was officially published in book format by Woongjin ThinkBig under the Funnism label (재미주의) from April 30, 2018, to October 25, 2018.