| "I once thought I could save the world... now look at it"
— Spoilers for Deus Ex: Mankind Divided follow!
If you do have the cure and want to save everyone, including Miller (and get the He's [Not] Dead, Jim achievement) you can do it if you move fast. However, this walkthrough will assume you do not have the cure (if you do, you can go ahead and use it now on Miller).
If you choose to save the delegates first, run through the door in the back of the catering room into a heavily guarded area. You can either sneak through vents, fight your way through, or, if you have a ton of biocells, the Icarus Landing, maxed out leg augmentations, and maxed out glass-shield cloak, you can run through without raising suspicion (you will need about 20 biocells if you run through, just to be safe). The most straightforward path is to run down the hall with the 2 cloaked guards and turret, down the hall to the right and towards the marker that will take you to an elevator. If you do not want the guards becoming suspicious or alarmed, do NOT call the elevator. Instead, go through the door that is next to the window with the keycard and use Icarus Landing to jump down the elevator shaft and enter through the open hatch. Take it to the VIP rooms. If you gave Alex the evidence from M7: The Rucker Extraction, she will tell you a code for the door you will need to get through. Get to the floor and run down the hall to the locked door. Use the code, a multi-tool, or just hack it to get in and a cutscene will play out. If you were quick enough, you will stop them from taking a sip.
Now, once the delegates have been rescued, run back to the elevator but do NOT take it the other floor if you left the guards there and do not want them becoming suspicious. Instead, exit up through the hatch and out the door you came through earlier. If you are moving fast, this is when Marchenko will comment that you are taking awhile. The marker is going to look confusing here, but you just need to run back to the reception hall, so run back the way you entered however you see fit, back through the catering area (Miller doesn't have anything else to say if you saved him) and jump down to the main floor of the reception hall. Go through the doors on your left and follow the marker all the way around to the exhibition hall and enter. If you were fast enough, Marchenko will be none the wiser that you saved the delegates. There are several quick options (both lethally and non-lethally) to take him out, like if you got Allison Stanek's switch or Damocles' Sword (Marchenko's killswitch). Take him out however you see fit and the game will switch to the ending, giving you the achievement.
Alternately, if you choose to face Marchenko first, walk back to the reception hall and the door to the exhibition area is now accessible. You can walk straight to Marchenko without meeting any guards. Once the fight with him is triggered, go to the second floor, cut through the security room (with the dead guards), and crawl across the beam to the other side. In the area with the sentry turrets and the mine, there is a switch underneath the bar table. Pulling this switch will open up a secret entrance to the VIP area. Once you save the guests, turn back through the exact area you came in (look at the minimap if you are lost) from and continue the fight.
Tips and Strategies Edit
- There are a number of factors that wil decide how easy or hard this will be to get. However, it is highly recommended to do M17: Protecting the Future first, especially if you do not have the Orchid cure from M12: The Heist. Reason for this is that if you are too slow in dealing with Marchenko, by the time you make it to the delegates they could have already drank the Orchid and so you will need the cure to save them. If you are too slow, they will already be dead.
- If you did not set off any alarms during M15: Securing the Convention Centre, you will have 10 minutes to save the delegates and run to meet Marchenko. If you did set them off, Marchenko will give you less time (unsure how much less).