When you return to the Old Town Tower you talk to a bloke named Noah who tells you about distress messages from women and children in the Fan Zone. They are willing to trade supplies for help - and we should check that out.
I don't know about you but this sort of situation makes me nervous - after all, how many great Sci-Fi stories begin my luring in a rescue party with a distress signal??
When you get to the building and inside you use the lift to enter the Instance Zone - this is a venue center it seems but, once you get inside and, what did I tell ya! You turn off the recording and the voice then starts telling you - via the PA system, that it was indeed a trap!
He plans to kill you for your stuff mates!
After you go in the lift climb on top and go through he ventilation ducts - the nutter has set fire to the floor and is wearing a breathing suit so you are at a disadvantage here - you need to kill him - quickly! But his suit seems to be part armor and he is a bit on the difficult side to kill.
The easiest way to do this is to kill him with a headshot - that pretty much ignores the armor.
Turn the power back on to get rid of the smoke, then take the lift to leave and you will complete the side-quest.