1 - Follow Hakon
Meet Hakon. He's your new bestie in town. You need a Biomarker to progress.
Follow him over the roofs until you're out of stamina to do so. He will help you up, but you will have to get an Inhibitor too.
Lucky that it is both in the same location...
2 - Search the roof for loot.
You stop at a Roof Grove. Tall trees that mark loot and crafting materials. The loot that makes your quest continue is in the big box in the small hut.
3 - Follow Hakon
Continue to follow Hakon. He will stop to introduce you to a faction called The Peacekeepers.
After that, continue to follow him to the roof where he wants to loot a big airdrop box.
4 - Search the Airdrop
The box is empty but you can use the GRE key Spike's contact gave you in the tunnels.
You can use it to open special doors and boxes in the future.
5 - Get to the Safe Zone
It's getting dark and you are introduced to the UV light. You're are safe in an UV light area.
Follow Hakon to the Bazaar, the big settlement in the Trinity Territory. But they won't let you in without Biomarker.
Escape the zombies to the next location and fight them off until you are let in.
You'll be spotted by one of the screecher zombies and a chase starts.
6 - Follow Hakon
Follow Hakon back onto the roofs while being chased.
Talk to Hakon when you arrive at the door.
7 - Kill the Virals / Help Hakon
Fight off the Zombies while Hakon negotiates. Talk to him when the fight is over.