Walkthrough:
1. Read the letter (Upper left corner). First characters of uncle's name(A=1,B=2...) is the code of door's padlock
2. Read a book on the bed. Go back to the previous room and find an active spot on the floor. There will be chalk(gem) there
3. Click on the pictures, there will be a description of the number and element depicted on the safe. Use them to find the password and read the note.
4. Go to the bookcase and read both shelves. Serum recipe, it's casual color mix"Orange=Red+Yellow"... Demonic vol.13 red parts it's signs find in shelf with many drawer(near bookshelf), remember the drawing
5. Mix the flowers on the chemical table and then heat them on it(quick time event)
5. There is a lighter in the chest of desktop, take it.
6. Click on the clock in the center of the room and see what position the hands are on the dial. Go to the room with the altar and light the candles in the same way
7. Draw a picture from the Demonic vol.13. Didn't succeed? Then paint the edges so that you can be sure
8. Go back to the table and look at the paper with the table. These are ordinary linear equations. Just choose variables like X, Y, Z, N and calculate X+Y=10, X-Z=1 ...
9. In Demonic vol.13 you can see the correct word order for a particular demon. Just repeat it. And summoning compleate