Well, the alien planet of Celerion had been invaded by The Xir'algath, who wiped out the entire race.
Our heroes, after wandering through The Multiverse and trying to get back to their home, end up on Celerion after meeting up with the Angels.
Now, we are about to meet a whole new character...
That's the simplest explanation I can give without making you feel confused or out of the loop.
If anyone else wants to add in other details, please feel free to do so.