I'd have to say it is the conclusion of Galen Beckett's Wyrdwood series, The Master of Heathcrest Hall. The first in the series was The Magicians and Mrs. Quent, the middle volume was The House on Durrow Street. I highly recommend the whole series - its a mashup with magic, fantasy, theatre, and Regency romance, and was creepy, gripping, and romantic. I found it by accident, and I never understood why I heard so little about this series! (Beckett is actually the nom de plume of author Mark Anthony). Find more at http://wyrdwood.net/mrsquent/ .
