OOC:
Yes, the adventure doesn't indicate how you know this, but the Mask is clearly the key to this mystery.
Shardizhad the crystal dragon is delighted that you return the compass to her, and offers you a bargain. She'll buy the compass gem back from you for 1350, keeping the difference as her profit.
Later, at the Grand Mausoleum...
Sebti the Crocodile
After some high level Divination,
"The mask is the Mask of the Forgotten Pharoah. It's the repository of the a piece of the essence, or ka of a powerful individual. By the right of the Pharoah, the current one, it is yours. But first will you allow us to use it to reverse the terrible effect of was used for?"
Fortunately, the church of Pharasma can conduct a ritual to lay all of the undead raised by the ka pulse to rest. Once the ritual is completed, the church can begin the somber work of returning the dead to their graves. The Voices of the Spire turn their attention to maintaining peace among the living and assisting in the city’s recovery, and any psychopomps remaining within Wati are sent back to the Boneyard.
At this point, the city’s Panic Level automatically decreases by 1d4 points per day until it reaches 0.
Congratulations, you are level 7!