Do three issues make a “saga?” I don’t know. But that’s how this is billed. It’s a big, cosmic story.
Starfox, who has been pursuing Nebula across the galaxy in the company of Firelord, comes to Earth and tells The Avengers that after the planet Xandar was wiped out by Nebula (in Avengers #260, which led to he and Firelord pursuing Nebula across the galaxy, Super-Nova, the last survivor of Xandar, is holding Firelord hostage.
It’s not clear to me why, but I guess it’s because Firelord used to be associated with Nebula.
The team fly out to space to help, and do manage to rescue Firelord but in the process they reveal that Nebula, who Super-Nova also holds responsible for the death of his planet, is on Earth.
They also get attacked by brain leeches.
So, Super-Nova goes to Earth and the cosmic battle is brought there. He gets there before The Avengers can get back from outer space, and so Quasar rises up to fight him, alongside the West Coast Avengers and the Fantastic Four (i.e., the team led by Thing that doesn’t include Mr. Fantastic or Invisible Woman).
Eventually, the East Coasters get back from space and Super Nova is defeated. Actually, he’s diverted. Reed Richards figures out that Super Nova should go after Nebula via the time stream and prevent the previous destruction of Xandar. Kind of a weird ending, to have Reed Richards enabling someone to change the time stream.
These issues are used to spotlight how the slapped-together team isn’t working right—mostly, it’s because Reed Richards keeps acting like a leader (when Captain America leads this team) and Gilgamesh is a muscle-bound, punch-first-think-second idiot.
From here, there’s a back-up in Avengers Annual #18 where Quasar joins The Avengers, immediately after the end of issue #303.
Creators: Mark Gruenwald (plot), Ralph Macchio (script), Bob Hall and Don Heck (#301), Rich Buckler and Tom Palmer (302-303); Avengers Annual #18: Mark Gruenwald, Mark Bagley