At the start of the game, everyone is attending a picnic in honour of Sonic’s 20th, when all of a sudden a mysterious dark force intrudes and sends everyone, including our spiky blue protagonist, back in time. Sonic is finding a way to get himself and everyone else back to the present time and along the way he bumps into many familiar faces including his younger (albeit chubbier) self! The two Sonics team up and work together to save their friends once again.
All About Games article.