Use the Whistle of the Freethinker to speak with Brand on the steps outside the Castle Mistmoore ( 683, 187, 105 ) /waypoint 683, 187, 105 He sends you to the castle guest quarters for evidence.
You can choose to get to the guest quarters one of 2 ways:
If you go in the front door, proceed to the chapel area at the back of the main piano room and head down the stairs. At the bottom of the stairs is a room with several linked Epic x2 mobs, assorted Heroic ^^^s and occasionally the Count of Somnborn. The guest quarters are off the side of this room down another staircase and right, down the hall.
You can also approach the guest quarters from the bottom coming up through the catacombs. Take the hall south from the spiral staircase, proceed up and then West at the T intersection straight past the Maid's room and the Fountain room will be the guest quarters.
The first update is an autoupdate obtained by entering the Guest Quarters ( -73, -5, 71 ) /waypoint -73, -5, 71.
The second update is in Graf Korban's room in a chest ( -24, -4, 54 ) /waypoint -24, -4, 54.
The third update is in Voevoda B'Aelsqui's room in a wardobe ( -42, -5, 42 ) /waypoint -42, -5, 42.
The fourth update is in Viktor T'Hoth's room. It is a book on a nightstand ( -93, -4, 43 ) /waypoint -93, -4, 43.
You must now go back to all the rooms to plant the evidence by switching it around.
Return to the Graf Korban's room and place the found letters by clicking the bedside table ( -21, -4, 55 ) /waypoint -21, -4, 55.
Next, go back to Voevoda B'Aelsqui's room and click on another bedside table ( -47, -4, 40 ) /waypoint -47, -4, 40.
Then, go back to Viktor T'Hoth's room and click on the desk to the left of the door as you enter to get your update ( -71, -5, 55 ) /waypoint -71.3, -5, 54.6.
Return to Brand for a new enchanted flute and Freethinker status. The next quest begins in Castle Mistmoore.