Shadows House follows the uncanny daily life inside a colossal manor hidden deep in the mountains, far from ordinary human society, where the Shadow family of nobles lives in constant secrecy. The Shadows are pitch-black beings who release soot when they are agitated, and when a child of the house comes of age, they are paired with a Living Doll: a human attendant who serves as their face, their voice, and the second half they can never show, the expression they might have had if not for their dark complexion.
Emilico, a cheerful newly created Doll, is assigned to the soft-spoken Kate, and the two quickly form an unusual partnership despite their very different personalities. As Emilico learns the rules that govern her role and tries to carry out her master's needs, she begins meeting other Dolls and their respective masters, slowly piecing together how the manor's society works and what is expected of those who live within it.
Guided by the rule that Dolls must not fret over trivial matters, Emilico still finds it impossible to ignore the strange customs, hidden tensions, and deep secrets surrounding Shadows House. The more she discovers, the clearer it becomes that the estate's elegant routines conceal a far more disturbing truth about the purpose of the Dolls and the world they inhabit.