Missable! On your 2nd visit to Hengsha, head to the LIMB clinic and speak with Dr. Wing, who gives you this sidequest. He will ask you to deal with a rogue Belltower operative team, led by Michael Zelazny, supposedly hiding behind a butcher shop in Youzhao District.
Upon reaching the butcher shop, open the storage door and head down to find a dead soldier. Read the Pocket Secretary on him to find that Zelazney has gone underground into the sewers. The entrance to the sewers he is hiding in is located in the Dongbai district, where the main objective of the sidequest “Corporate Warfare” takes place, and not far from where you found Ning in “Rotten Business”.
Head down the sewers, take the first left and climb up the ladder to end up on a ledge overlooking Zelazney and co. There is only one way to approach them - from the front, but here you can throw a Gas Grenade and knock all of them unconscious, which completes the objective and without needing to fight them.
Alternatively if you do go up to him, answer any of the following:
"Inquisitive, No, Inquisitive, Inquisitive, Inquisitive, Reason, Let Go"
"Inquisitive, No, Inquisitive, Inquisitive, Inquisitive, Approve"
if you want to avoid a fight. Head back to Dr. Wing for the trophy and a PRAXIS kit.