“Secret Investigation” is a side quest in Wuthering Waves where you will be helping Qianshan investigate the exile camp near Lake Deerslumber. This quest will reward you with the following:
500 Union EXP
40 Astrite
2 Advanced Resonance Potion
1 Advanced Sealed Tube
24000 Shell Credits
Aside from the rewards mentioned above, you will get the trophy “Sorry, I’m a Patroller” after completing the quest.
How to Begin Secret Investigation Side Quest
To start the Secret Investigation side quest, you must find Qianshan He will be near the northwest of Lake Deerslumber. This side quest will automatically appear on your map once you are near the area.
Get Exile Clothing
The Exile clothing can be found in two marked locations on the map. Defeat the Exiles near the area to collect the top and bottom clothing. Once done, go back to Qianshan for the next part of the plan.
Discuss your next plans with Qianshan
Next, speak with Qianshan again. He will discuss the profile of the person you pretend to be, Qiao Yang. Qianshan will question you about the profile, but no worries if you get the answers wrong; this doesn’t have any consequences.
Investigate the Exiles’ Camp
To investigate the Exile camp, the time needs to be set at 21:00. After changing the time, go to the Exile camp. Once you are there, your character will change into an Exile outfit. Talk to the Exile guards.
To change the time, click on the Terminal 
and look for the Clock icon 
at the bottom of your screen. Click on it and drag the time to the desired time and click confirm.
Find the elevator
After talking to the Exile guards, you will be denied access, so you need a new way to infiltrate the camp. Go to the marked area to access the elevator. Avoid the dogs and Exiles with the eye icon, as you must repeat the process if you alert them.
Make Kukixiao leave his post
Get up the elevator. Once you got up, you need to make Kukixiao leave his post to retrieve the notes. To do so, you need to answer his question correctly. Respond to the second question with “Both of us are not fans of hot food” to make Kukixiao leave, and now you are free to take the notes.
Distract Xiyun
After taking the notes, you must access the data that Xiyun is guarding. You must destroy the signal transmitter to distract her, and she will leave the room she is guarding. Now, go to her post and begin transmitting the data.
Defeat all the Exiles
When you leave the area, you will see that Exiles surround you. Defeat all the Exiles in the area. Once done, report back to Qianshan, and the quest will end there.