It's really not that hard. Just never fight, but run away and hide instead. If you can't make it, just reload last checkpoint. After every single investigation there will be a new checkpoint. So i.e. you do the first messenger first, get the letter and then try to do the eavesdrop but fail it, you can reload last the checkpoint and it will put you back to the harbourmasters hut from the beginning. But you will still have the first investigation completed. I purpously failed, to check if that works, and it does. I had to reload checkpoint one more time, during the eavesdrop mission, because guards started attacking me. It was the fourth investigation I attempted, and after reloading, it still said that I have 3/5 completed.
Whenever I got detected during the fishermans objective, I just ran away and hid.
After I've done all 5 investigations I went back to the brothel woman (also DO NOT fight anyone on your way there, even if you are technically not investigating anymore) and the mission was 100% completed.
- never fight guards (no matter if you use lethal or non-lethal weapons, just never fight)
- reload checkpoints when needed
New XBL Profile since October 30th 2013.
Completed Retail Games (includes all DLC): 16
Completed Arcade Games: 18
Completed Xbox One Games (includes all DLC and Apps): 5