The fallen make one last attempt to take the last city. They breach the walls and the city must make a final stand. Lord Saladin must rebuild the iron lords to assist us in fighting back the fallen. The fallen throw everything they've got at us. The raid will take place on earth, and will be under siege, much like the crucible map "memento" shows. The final boss will be a either a supreme servitor, Randal the vandal (again), or literally a fallen ketch. It will set the tone for destiny 2, where we begin with the city having a great victory under their belt, and prepared to take on the rest of the darkness. Unless we are in fact the darkness (illuminati confirmed?)