From Destinypedia, the Destiny wiki
All dialogue is spoken through the Ghost's comms.
The Guardian is at Firebase Rubicon, where the Cabal's base is filled with multiple supplies and barricades, presumably to help the out their fellow soldiers, who are at Rubicon Wastes.
The Guardian then defeats any future Cabal reinforcements, and leaves the base, as they head into Rubicon Wastes, where they face off against a Wolf Walker.
The Guardian then battles and destroy the Wolf Walker, along with any Fallen or Cabal soldiers, who were there.