After you have sufficiently explored the entire estate and the adjacent garden, go to the room located in the North-Western part of the first floor, to the library shown in the above screenshot. You need to watch out here, because there is a single guard here and a female servant. As much as possible, try to search the library in order to obtain the Baron's Bust - 25G, a Candlestick - 15G and a Tea Pot - 5G.
While exploring the library, you should avoid detection by one of the characters, while waiting for a good opportunity to rob the guard of his two Coin Purses - 2+7G. It is worth adding that you can make it easier to stay in shadows, by using the water arrow to put out the fire. After you have explored the area, go to the other end of the library (make sure that you do not walk over the shattered glass!) and give a row of books a quick examining, thanks to which you will find a switch that will open a secret passage. Go to the elevator here and get to a higher level. Follow the empty corridor and press the button that unlocks access to the Architect's study. [Eastwick's Grand House - The Study].