This mission starts at X: 600.8, Y: 796.9 , from a woman inside one of the buildings. She wants you to find her husband and see if he is committing adultery. You need to find him in one of the buildings, but you need to be sneaky about it, so crouch and walk around that way. If you get too close, a timer will appear and you’ll fail if it reaches zero.
Get close enough to the window to overhear the conversation, revealing he is cheating, but not with a woman. You can either confront the husband or tell the wife; the choice doesn’t matter and the mission will end after talking to either. Your reward is $500.