This movie brings to mind the hey day of early seventies low budget British shockers from the likes of Amicus, Tigon, and Hammer. The days when all you needed to make a film was a spirited cast, a largely unknown bolstered by a single "name" performer recognisable to Americans (in this instance James Cosmo), and free access to a down at heel stately home.
It's hard to classify this movie in terms of genre, neither truly a thriller nor a horror. – it's more of a "creeper" than anything else. The sense of unease is ramped up throughout the convoluted twists and turns of the plot before plunging into true horror in the final third.
I think this has presented a problem for the marketing department and I feel that they may be making a mistake in the way that they are presenting it. Many people will feel mislead and disappointed that this isn't the horror movie that the posters suggest, which is a shame since it's more than that, it's a taught, well acted chiller that deserves to be more widely seen.