Start by going around the building on the right and into the next room. Move up to the second floor, defeating the Cabal as you go. A Major Centurion drops into the room with a Legionary. You’ll need to take it out then deploy your Ghost to get the location of the Skyscraper. Head out the window and into the side door below. There are plenty of Cabal here to welcome you then after, just follow the corridor down into the Dust Palace.
Dust Palace - Darkness Zone
There are plenty of Cabal ahead in this area but there are also so many places to duck and then pop out for Precision Damage, that the number of enemies becomes negligible. Follow the signs into the atrium where Vex spring into action to attack the Cabal. Ignore them or kill them all then fight your way to the Overwatch.
You are met by a Colossus and Phalanxes. Behind them are Legionaries who would try to stop you. The middle area is fairly open with small walls for cover. Use this to your advantage and take out the Psions and Phalanxes from behind. A Major Centurion drops in towards the end so deal with it using Heavy Weapons and Super Abilities as always. Return to the Cryptarch once completed.