Securing the Convention Centre

M15: Securing the Convention Centre is the 15th main mission in Deus Ex: Mankind Divided, and the first one to take place in London. Adam Jensen flies with TF29 to the Apex Centre to try and stop Viktor Marchenko's, and therefore the Illuminati conspirators', plan.

Meet Liam Slater in the C.S.O.
In London, you’ll meet and briefly talk with Nathaniel Brown, who refuses to cancel the event regardless of what you say, so Jim Miller decides TF29 needs to do their own sweep and Brown agrees. He'll then tell Adam to work with Tarvos Security to make sure everything is in order. You can explore the top area around the helipad if you want, but there’s not much to find. Make your way to the elevator and head down to meet with Liam Slater, the one in charge of convention security. Adam will contact Alex to keep her up to date, but Janus will respond and say the UN delegates are of the utmost importance as the Human Restoration Act cannot pass. You’ll then reach the security level.

In the initial area there isn't much to explore, but you’ll find a vent behind some vending machines that can lead you into the next area or the security room. It’s heavily advised if you’re doing stealth to go into the latter and shut off everything you can. Go talk to the guy behind the window where Adam starts to have a suspicion something isn’t right. You can choose to outright attack them or decide to be more discreet (trick or back off result in the same thing, though the first will make the guard behind the window walk off). Adam will then notify Miller about his suspicions and Duncan MacReady points out similar thoughts as nobody from Tarvos Security on his end have contacted him yet. Miller then tells Adam to get to Liam Slater's office to see what's going on.

Get to Slater’s Office
If you hacked the security terminal earlier, you’ll have to go back and turn off the 2 cameras that turned back on if you want to take out the guards in the front without alarms going off. As MacReady can’t move any further into the building due to being locked out, Adam has to get to Slater’s office to override the security shutdown to let the rest of the team in.

Activate the Security Override Switch
If you do some exploring in the area, you’ll confirm your suspicions when you find dead Tarvos Security guards and gold masks in some of the rooms and this part of the mission will activate. Get to Slater’s office and you’ll find the code for the switch on the unlocked terminal. Once overridden, you’ll see Brown pop up on screen as he talks a bit in the reception hall before Adam notices the terrorists are slipping in through a back door near the catering area.

Find the Keycard to Catering
Now get back to the elevator and head to the reception hall. Miller will tell Adam to take out all the reception hall guards quietly, and find the keycard to access the back area. Taking out the guards is optional, but if you don’t take them all out an alarm will be triggered later, so if you’re going for the Foxiest of the Hounds achievement, take them all out quietly. A few tips on taking them out without causing an alarm or panic: If you don’t care to take out all the guards, you can find the keycard 2 ways: on the guard using the restroom or, with the klipsringer aug, travel in the vents that connect the restrooms to jump up into an area of the ducts where you hear 2 guards talking and move around until you’re near a damaged vent opening and you’ll see a keycard. As soon as you get the keycard MacReady will be out of commission for a little while due to tripwires in a stairwell.
 * Mind the cameras and guests watching.  As long as the guests don’t see you do a takedown, or the cameras don’t spot a body, you’ll be fine.
 * Some reason guests don’t freak out if a guard suddenly goes limp and falls over from a tranquilizer, so use that to your advantage.
 * Naturally, other guards won’t react so well if they spot a body and will sound the alarm and attack.
 * Don’t drag bodies if no other guard is in the vicinity in the unrestricted areas, as guests will then decide you’re acting suspicious and panic.

Investigate the Catering Area
Make your way to the secured door and head through and you’ll find out you can’t get a hold of Miller, but MacReady can read you. Continue through towards the marker. If you didn’t grab Damocles’ Sword during G.A.R.M., this is the area to grab it if you want to use it in the final fight. It’ll be in the room past the catering area (around the corner), in a box under a desk. Enter the catering area and a cutscene will play out. Now you have a hard choice to make...