A Not-So-Happy 18th Birthday

Sonic's dark past has come back to haunt him, but he has found Robotropolis again! But Eggman kidnaps Sonic's siblings, and every time Sonic rescues them, Eggman snatches them back up!
What is Eggman up to? What does it have to do with the "Flames of Disaster"? And why is he trying to expose Sonic's deepest secret?
Also, what's gotten into Shadow? Why is he being so nice to Sonic?

I originally posted this story on FanFiction.Net and it was pretty popular.