Rotten Business

Rotten Business is an optional side quest in Deus Ex: Human Revolution, and has a similarly named achievement/trophy for completing it. It is given to the player by Mei Suen.

Introduction
Mei, one of the senior prostitutes working at the Hung Hua Hotel, has a problem: one of her friends and coworkers, another prostitute named Ning Tsai, has gone missing. Mei suspects foul play - augmented prostitutes bring in more business than normal ones, and under the iron fist of Diamond Chan, the new Hengsha underworld kingpin, girls have been undergoing augmentation by force. Mei needs help finding Ning and dealing with Chan.

Overview
Jensen must find a prostitute named Ning who has gone missing. Mei suspects foul play. After finding her, Mei needs Jensen to find Diamond Chan and put an end to his reign once and for all. She needs him out of the picture permanently, which means either his death or a conviction - either method requires Jensen going to his apartment and dealing with him.

Ning
Mei suggests talking with a bouncer named Chuanli, who might have information on Ning's whereabouts. He is located on the roof of the Hung Hua Hotel and must be either bribed or persuaded to give up what he knows - that Ning is located in a side street near the Daigong district. If the player bribed him, they can retrieve their money by simply knocking him out or killing him and searching his body. (If you have the Social Enhancer Augmentation then you will be prompted to use pheromones when the option to bribe him comes up, select the option to appease his Alpha personality and he will give you her location without bribery.)

Upon reaching the lot, Jensen finds that Ning has three armed guards that must be taken out. After disposing of them, Jensen will find Ning in a storage, frightened but unharmed. Jensen should then report back to Mei.

Storage door code is 5377. The code is found in a pocket secretary on one of the thugs.

Chan
After helping Ning, Mei turns her sights to Diamond Chan - as the new kingpin of the Hengsha underworld, he must be swiftly dealt with so that the prostitutes can go under new management. She needs him out of the picture permanently, which means either his death or an actual conviction. If Jensen opts to go for his conviction, Mei will give him a package of drugs to plant in Chan's apartment. Either way, Jensen will need to go to Diamond Chan's apartment in the Youzhao district.

Diamond Chan is alone and has no bodyguards, but he is armed. Jensen must take care not to kill him. In addition, he cannot leave evidence of foul play, so using non-lethal weaponry is out of the question - the only option is a non-lethal take down. After incapacitating Chan, Jensen needs to either assist in his 'suicide' or plant the drugs.

The easiest way to get the drop on Chan is to crouch and take cover beside the door, then open it. It will draw Chan's attention. He will not leave his apartment, however, and decide it was nothing after a few moments, then put away his weapon and turn around. While staying crouched, sneak up behind him for the takedown.

Alternatively you can get close to the door and overhear his phone conversation, after he has finished you can wait for him to move away from the door and sneak up behind him and knock him out.

If the player wants to kill Chan and make it look like a suicide, Jensen needs to drag Chan's unconscious body to the outside roof and drop him, and he will die from the fall. If Chan is to be convicted, Jensen merely needs to plant the drugs in his coffee table and leave. Either way, Jensen can then report back to Mei for his reward.

Shooting Chan's unconscious body after planting the drugs will reward with an extra 300 XP and will not void the other quest rewards, making this option the most lucrative.

Reward
For either planting the drugs and throwing him off the rooftop, the experience reward is 1000 upon completing the mission, not counting various bonuses for completionist at all.

Mei will reward the player with 1000 credits for saving Ning and a further 2000 credits for dealing with Chan.