It's been awhile since I've read a good Gothic. From the description, I thought this could be one. Well, nope. The paternity mystery is easily guessed. Convenient end with the villains. This was very dry and dragged for me.
A complaint. If given a key to a room that has been LOCKED for YEARS, wouldn't you make sure said door was LOCKED again when you left?! Or at the very least make sure the damn door was closed?! Stupid.