It's Sonic's birthday, and all his friends have thrown him a surprise party. Unfortunately, just as the celebration gets underway, a mysterious creature appears in the sky and pulls Sonic and his friends into strange interdimensional portals! This strange creature is wreaking havoc on the time-space continuum, and Sonic along with a younger version of himself end up at the crossroads of time. The two Sonics must work together to restore his history, save his friends, and fix the flow of time!

Sonic Generations is a fast-paced action platform game in the long-running Sonic the Hedgehog series. As part of Sega's 20th Anniversary celebration for the character, it revisits the history of the entire series with famous stages from all of the major titles over the last 20 years. The game is divided into three "eras", each with three stages, which each come from a different game starting from the original Sonic the Hedgehog all the way up to Sonic Colors, and including many of the highs and lows in between.