The game 'Le manoir de Mortevielle' is quite quick to finish but the solution is really hard to figure. I'll just tell you what items you need to find and how to use them but not where they are to let you sneek around a little in the manor.
The first two items you need are presents from Julia to his family members: the ring with a cross and the dagger also marked with a cross. Once you've found these go to the crypt. Use the dagger in the symbol on the center of the wall (there is a darker line somewhere near it) and enter the secret room. Put the ring in the orb and turn it. I don't remember exactly the verb you need to use at this time but only one works so save your game before this. A new secret place is now opened! enter and search the dead body. You should find a stick made of wood. Get it and return to the corridor. Climb to the attic and put the stick in the small hole on the furniture (some dark pixels). Turn the stick... you've won the game.Some questions may be asked to you to determine if you've successfully understood the story of the game like in 'Maupiti island', the follow-up to this game.
This solution is only based on my remembrance and might be incomplete. Keep in mind that I finished this game about ten years ago.
If you want to know more about the makers of this wonderful game go to their homepage: www.lankhor.com