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I assume you at the part where you need look for evidence so you need to sneak in to the harvest princess house at night you going to need ( sleep powder) or (shadow scarf) to get pass the guard up front right when you get pass there a open bag interact with the open bag to get the (windmill key) then follow the trail down stair then interact with the spot where the cardinal bell was suppose to be to start the next quest which is the go to the windmill (during the day).