I'm in Eastwick's Grand House trying to get past a room with a patrolling guard and a servant, who are having a conversation. On the other side of the room is a secret entrance in the form of a bookshelf. There's a bird in the corner on the right and pieces of glass in the corner across.
I tried to sneak past following the guard's footsteps, but the servant is looking at the bookshelf almost constantly notifying the guard when I try to open it.
How do I get past the room undetected?
By far the easiest way to get through undetected, is by climbing on top of the shelf on the screenshot's right and remain on high-ground, until you reach the shelf the maid is currently cleaning. From there, jump off, find the switch-book and pull it.
If you still have problems getting past this, (and if I recall correctly) (spoiler):
beyond this bookcase is an elevator. The waypoint is up, but the elevator goes down as well. Since I discovered this from the elevator itself, I am unsure if the lower access is openable from the lower floor or if this was intended to be an egress only.
The way I did this, was to shoot at the fire with a water arrow from about where you are standing in the picture, while the guard was standing and looking at the bookshelf to the right (where he walks away from in the picture). This will prompt him to light up the fire again.
Then, before the guard actually starts moving to the fire, hush along the fireplace where you are now fully invisible. Then quickly find the book in the bookshelf, while the guard is still busy with the fire.
The easiest way to do this is by using a hidden passage under the house to bypass the room completely. (Though this is a bad idea if you're going for full loot.) To access this hidden passage, enter the greenhouse on the left when you first enter the area. There is a misplaced brick on a wall inside the greenhouse. Use the brick and you will enter the passage.
Warning: The passage is full of traps, but you can avoid them without disabling them.
The linear passage eventually leads to the space behind the bookshelf in question.
You can also bypass the bookshelf path by going through the kitchen cellar. The kitchen is the left room at the bottom of the main staircase; you just need to get past the two patrols and the cook. There is a switch in the cellar that will open the wall allowing access to a narrow passage on the other side. Heading right will lead to the space behind the bookshelf.
