An alternate timeline where Infinite gave his soul to become one with the Phantom Ruby, corrupting the world and its inhabitants with the ruby's powers.  You, along with some others, are the last ones uninfected, but things are rough.

Sonic: Missing, has been gone 2 weeks on recon
Knuckles: Infected, Stage 2 (corruption has made him see friend as foe, taken both his eyes and his speech)
Tails: Alive, lost arm to Knuckles
Amy, Blaze: Dead
Cream: Alive, heavily injured and mute
Silver: Erased