How do I find out about it?

Hint 1 of 5:

Who is researching into things related to Master Lu?

Hint 2 of 5:

Baron Von Seltsam was, but he's dead now.

Hint 3 of 5:

If you can't ask him, rifle through his mail.

Hint 4 of 5:

The letter may be where he spent most of his time.

Hint 5 of 5:

It wasn't in the billiards room.