Find the Wizard. (In a corridor headed to the pools around 30, 7,-93, a text message reads, "You see footsteps leading to the edge of the water.")
As you approach the island with the blue torch he will spawn and attack you as soon as you are within range. He's a 22^^^ with a 22^ familiar that you must kill as well.
This encounter will break any invisibility/stealth you may have going, so be prepared.
After reading the letter you discover that the wizard is using his familiar to spy on someone named Kan(bloodsmear)phon, and that this person is entering Neriak through tunnels in Fallen Gate. You should tell Zaveda of your discovery.