It won't necessarily help if you're aiming for the rewards, but you can reset the quest progress and start over from the beginning by talking to Maria outside and picking 'Reset my replay progress'.
As for the gems... I hate to ask, but is there any chance that the gem you're missing could be the one on the floor of the statue room?
If not, these are the locations of all the gems-
-Inside the clock in the starting room (1 gem)
-Received from completing the book puzzle (2 gems)
-In the puzzle room with the suits of armor (1 gem) (could be this one - I actually forgot this one on my most recent replay and had to go back for it)
-Received from searching the faceless servant on the other side of the curtain (1 gem)
-On the floor of the first one of the statue rooms (1 gem)
Later, for your second trip, there are two more gems-
-Found on the skeleton in the room accessed with the piano key (1 gem)
-Found on the corpse of the thief in the hidden room, beneath the room next to the statue rooms (1 gem)
29-Jul-2022 05:47:06
