He has left some instructions on how to open his safe, you’ll find them on the right side of the shelf.
From the instructions you’ll find out that there are three cylinders that are also numbered and each of them there is a puzzle that shows one of the combination codes. Leave the room and go to the counter to the left, where you can see a painted board in the back corner. Turn one side over and collect the three cylinders.
Now, head to the room with the gramophone and listen to the recordings on the cylinders. These are the three puzzles and solutions:
Cylinder 1: And these Red Drops, like precious stones, lie fixed, set in divine gold. To be the guardian of the grail does not protect me from its attraction, Henry. And I do confess it: I am willing to pay to know its secret.
With these instructions, it should not be a problem for you to find out the safe combination. The first cylinder refers to the golden goblet, which is located in the same room as the gramophone. Go to the window and examine it. For the first number you have to count the red stones on the chalice.
Cylinder 2: I finally understood that we were only pieces on the chessboard of the gods. Let those of us who are still standing protect our white queen from their soldiers. I see our number dwindling and my will strengthens as my apprehension grown. We shall refuse to be the playthings of destiny.
The second cylinder will guide you to the next number of the combination code. Drake speaks of a game of chess. In the same room where you also find the Gold Goblet, there is a table in the middle and a chessboard on it. Now you need to count how many figures remain on the board and protect the queen. Don't count the figures outside the board.
Cylinder 3: Dear friend. I thank you again for the anthology of the works of Arkham Editions that you sent me. Volume nine, Azathoth and other Horrors seemed particularly relevant to my research. I never tire of browsing through them.
The third cylinder tells you about a series of books and names you a particular volume. This volume is the last number of the combination code. As a precaution, search the books you find behind the counter in the entrance hall.
Once you've solved all the cylinder puzzles, you should now have the three numbers to help you open the safe. Now go to the room and enter the numbers 539.