Objective: Reach the mystery caller's signal source
Objective: Pinpoint the signal's location
Objective: Find and activate the ctOS Boxes
As you start this mission go straight through the alley and into the area. Lower the lift to the right, climb onto it, raise it and climb the platform to find a bunch of electronic parts for crafting.
Now head up the stairs to find the next waypoint and open the profiler to pinpoint your location. You'll need to find two ctOS Boxes, so hack the camera on the far right, moving it up and to the right to find an unlock option on the far balcony.
Now go back downstairs and head into the alley and to the right. Lower the lift here for a chemical component and look up to see a camera. Hack it and look up for another unlock point. Hack it and you've completed the objectives.
Objective: Access the building network to reach the signal source
Go back up the stairs to hack the box at the end and start another hacking minigame. Turn the left point three times and the point above it two times. The lower right point can be turned twice, then the point above it can be unlocked once and turned three times (four in total). The point in the lower left corner should be turned twice to unlock the final point which you should click to move on to the next hotspot.
With the second hotspot turn the far left point three time, the top point twice and the bottom point once. This unlocks the point above it and it can be turned once (two clicks in total). Turn the point on the far left once, the the points at the top twice and bottom point three times. Now unlock the point on the right to finish the hack.
Objective: Investigate the apartment
Objective: Hack the phone
Objective: Kill all fixers or escape
Objective: Follow the traced call to Damien
You have control of a camera in an apartment, hack the camera on the right, then the phone directly ahead. This attracts some unwanted attention so you now have a few options. You can escape, stay hidden in cover or kill everyone.
Using the cameras will give you access to explosive plates on the ground and explosives in the walls. You can raise a protector next to your location for better cover and take out any enemies who come up the stairs. If you use all the cameras in the area and blow up all the guards (including those holding explosives) you should be fine. Or you can use the explosives to clear a path and run down the alley, although this is considerably more risky.
Once you're done, get a vehicle and go to the next waypoint. Get out the car and up the stairs for a cutscene and the mission is complete.