Lady Avalon, there's a secret door on the east wall of the first room of the Shadow Thieves guild (where the thief selling stolen goods is). It will lead you up to a room where there is another secret door to the north. That will lead you to Aran Linvail.
When in doubt, search for secret doors! There are a LOT of rooms in that compound.
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Memnoch - Custodian of the Order of the Holy Flame 