At the start of the mission, go the restaurant, talk to the bartender, and pick up the toilet key. Go to the rest room and drop your Beretta 92SD there. Go out and to the north-east section of the map (near the sewer). Wait for the Red Triad Negotiator to pass near you. Go behind him and kill him with Oyabun knife. Take his clothes and Red Triad Amulet, then drop him to the sewer. Proceed to the restaurant.