Sophie has seen Cece sneaking out at night but wasn't able to find out what she's up to. Sophie asks you for help.
Quest Location
After you start the quest Team Cece or Team Reede?, talk to Sophie outside of Ventest Clothing to start this quest.
How to Complete the Quest
Sit by a fire until night, or go to the Hateno Inn and sleep until night. Then go into Ventest Clothing and wait for Cece to go outside at 10PM. Carefully follow her, but not too closely, and make sure that she doesn't see or hear you. She will go southeast, then will stop and look around at about 10:30PM. Then she will go south and around the back of the silo. Wait for her to go inside, and wait for the door to close behind her. Don't go through the door. Instead, go to the west side of the silo and use Ascend to get onto the wooden platform, then crouch to go through the small window. There will be a cutscene.
After the cutscene, it will be 5AM. Talk to Sophie in front of Ventest Clothing.
Quest Reward
Sophie gives you 10 Ironshrooms.