Received from: Reesa [Desert] (M20:15)
Reesa will tell you the whole truth about herself - she's behind all the murders. She will ask you for help with establishing Mirage's identity.
You refuse to help Reesa. You can return to commandant Valarin and give him the information on the murderer.
You will unlock [Murders Investigation].
You decide to help Reesa. Head inform Tongue (M20:40) that you are ready to finalize the transaction. You will find him inside a room on the first floor. Now head to the sewers (M20:41), locate Reesa [Hatmandor Sewers] (M21:10). Once you're ready, head with her to the meeting point (M21:11). A cutscene will start, after which you will learn who Mirage is.
SOLUTION 2- ENDING 1
After refusing to help Reesa, head to Basel [Desert] (M20:7) and collect your prize of 30000 auras. You can also refuse to accept the prize if you don't want it.
SOLUTION 2 - ENDING 2
In case you help Reesa, you will have to kill Mirage's right hand - Tongue. After finishing with him, you will soon find yourself inside Reesa's house, where the prize is waiting for you.