From Destinypedia, the Destiny wiki
All dialogue is spoken through the Ghost's comms.
The Guardian heads into the Iron Line. Dozens of Fallen await them. The Guardian kills them quickly. They continue toward The Legion's Keep.
The Guardian makes their way to The Legion's Keep, where Cabal and Fallen are fighting each other. The Guardian eliminates them, and the door on the far side opens.
Orbiks Prime appears out of the door. After, a long battle against the Prime, The Guardian destroys it.