The story takes place shortly after Sonic's last encounter with Eggman in Sonic Colors. In the past of Green Hill, Classic Sonic is exploring when he hears a noise, he then looks around but dosen't find anything. Suddenly, the Time Eater appears in the sky and he notices it, as the screen goes white. In the present day, Tails and his friends are having a surprise birthday party for Sonic, until the Time Eater appears and sucks all of them back into different periods in Sonic's history. Sonic goes to help but is instead attacked himself; he looks up before he passes out to see that Tails is the only one left struggling to resist the Time Eater's vortex. Sonic wakes from his unconsciousness in a white world with a colorless green hill zone, and wonders what's going on. Sonic first frees Tails when he was in a frozen state. Sonic and Tails then decide on finding their friends.Tails then tells Sonic to go check Chemical Plant out. Sonic quickly sets off, but a few seconds later, Tails sees Classic Sonic and mistakes him for Modern Sonic.