Okay. It sounds like you need one more in the kitchen/dining hall area, and then you'll be able to continue through to the next area. You may have simply not encountered it yet, or even if you did, it probably gave you some trouble. It's one of the more challenging and specific creatures to progress through so I'm not surprised if players are getting tripped up there.
To get through that particular encounter, you'll want to make sure you are thorough with your observation of the creature before you try any of your other options...
The basement is a mysterious place. The dim lighting, that guard standing watch... Rumors have been spreading among the mansion's guests and residents too...
(Hopefully those hints are enough to get you back on your way and enjoying it again. I tried to give you nudges without totally spoiling exactly what to do. If you still need more help just ask, and I'll be happy to clarify the steps needed.)