To begin with, the book was ill-titled. Poison does enter into the story but the house has nothing to do with it. Judging from the first chapter in which the protagonist- a scullery maid- adamantly and somewhat violently attempts to escape her (voluntary) life of servitude one might assume that her living conditions are dreadful. Dreadfully boring, perhaps, but really she lives a very ordinary life as a maid. Even better than, I believe. Apparently she lives in constant fear of a vengeful and mean-for-kicks housekeeper/relative of the estate's family. Sure, this woman is not to be liked. But she figured into the narrative mostly because the maid frequently complained about her. There were few actual confrontations with this woman and most of them involved her directing the staff on their duties. But the author was hell-bent on trying to pin every evil-intended thing on this woman for the sake of convincing the reader of her evilness and capability of murder.
The characters were without personality, the plot was predictable, and the ghost story was barely there and disappointing. The ending was nothing short of laughable as it was nothing more than a ridiculous Cinderella story disguised as a gothic horror story.