To find the safe, you need to get something from one of the other people in the house.
This safe is the nastiest slider puzzle I've ever run across. In the amateur version it's tough; in the master version, it's just sadistic. Read on for step-by-step directions.
What makes this puzzle harder than usual is that the tiles don't form a picture. Instead, the only way you know where they're supposed to go is by matching the little notches on the edges of the tiles to the notches on the frame. Yes, I said it was nasty.
The amateur puzzle isn't as horrible because it's only 3 by 3 squares, and when the puzzle is solved the middle square will be empty. It's still not easy, though, since you don't know which of each tile's four sides you need to match.
The master puzzle is 4 by 4, and the empty square will be in row 3, column 2. I go into a cold sweat just thinking about this horrible thing.
If you want to try it yourself, I'd start with the corners. Find tiles with notches that match each of the corners and start moving them. If they're right, the other pieces will be easier to find. Relatively, that is.
Here are the step-by-steps to get you through this nightmare; you might want to print them out so you can check off each step and keep your place. Save first, and save against instantly when it's done. (If you save in the middle, the game will reset when you load it in, so don't bother.)
The rest of the safe is much easier by comparison. You'll need the note you got from Charlotte's locket, called "Locket Note" in your inventory, for this.
Each line in the note is preface by two little designs that look like flowers. If you look back at the safe, you'll see those designs in the corners. So the first line refers to the top edge of the safe.
Count the switches, what the note refers to as levers, and click on the ones in the note. For example, in the amateur safe, the first line says 1, 3, 4, 5. So along the top row, flip the first switch, skip switch 2, flip switches 3, 4, and 5.
The four lines in the note go around the edge of the safe clockwise. It's not too hard to follow in the amateur game; the master is much tougher, but still not as hard as the first part of the safe.
You'll know when you have it right because the safe will pop open. Here's how the safe will look when it's finished:
After you examine the contents of the safe, things will happen automatically for a while. Hold onto your hat!