Stopping Marchenko

M16: Stopping Marchenko is the 16th main mission in Deus Ex: Mankind Divided, and one of the last missions (depending if you did M17: Protecting the Future) first. Adam Jensen must stop Marchenko from detonating bombs that will kill hundreds of people, but at the cost of the UN delegates lives and letting the Human Restoration Act pass.

Stop Marchenko Before He Blows Up the Towers
If you did M12: The Heist and got the Orchid cure, you can use it right after the cutscene to save Jim Miller (and get the He's [Not] Dead, Jim achievement) or, if you don’t think you’ll make it to the delegates in time, save it for them. Of course, if you do make it in time to stop them from drinking, then Miller will have died when you could have used it on him. This is typically why it’s better to save the delegates first if you have the cure so you can get the “best” ending and save everyone.

If you did M17 first, the marker may be confusing as to where to go. What you need to do is just get back to the reception hall, so go back down the hall to the doors you came through and past the catering area. Jump down to the main floor and go through the doors on the left and follow the marker to a set of doors which, when opened, lead to a cutscene confrontation with Marchenko who, if you were quick enough, will be none the wiser about the delegates being saved.

If you're doing this mission first and want to save the delegates as well, you'll have to take out Marchenko quickly. A few different options to do so are based on what you did in the game: Once you've dealt with Marchenko, if you haven't saved the delegates yet, run back to the catering area where Miller was found and through that door. Otherwise it'll cut to the ending and you can see how your choice play out in your conversation with Alex and on the news.
 * If you did M11: Confronting the Bomb-Maker and got Allison Stanek to give you the switch, you can use it to prevent Marchenko from detonating the bombs.
 * If you're not going for the Pacifist achievement and got Damocles' Sword (Marchenko's killswitch), you can use it here or anytime during the fight with him.
 * A quick way for non-lethal is to make a couple EMP mines and lure him in. When they go off, you can then run over and do a non-lethal takedown.