Quiet But Effective

Starting the Quest
Speak to The Mute in Shimmering Citadel.

Steps

 * Locate the secret chamber:
 * "Secret Chamber is where Mad Poet is in Poet's Palace. Lapis Scarab harvestable in the room" -- xKaoSx on official forums

Rewards
"reward is house item and 20 slot bag 35% reduction" -- xKaoSx on official forums