A mysterious creature known only as the Time Eater has managed to trap Zones from several time periods and dragged them into one white, bland world. This includes all the people that were in these areas to begin with, particularly Sonic the Hedgehog and his friends. Sonic must now work with an younger version of himself in order to save time and defeat this new evil threat.
As Generations is a compilation of the most popular levels from Sonic's history, there are several Zones that have also appeared in Sonic the Comic:
- Green Hill Zone
- Chemical Plant Zone
- Sky Sanctuary Zone
- Death Egg
- Stardust Speedway
- Seaside Hill Zone
- Mushroom Hill Zone (3DS version)
- Emerald Coast Zone (3DS version)
- Launch Base Zone (3DS version)
- Casino Night Zone (3DS version and DLC)
There also many others that have no connection to STC.
Many characters from the series make brief appearances in the game, mainly as advisors for particular levels. Naturally, some of them have appeared in Sonic the Comic, although they are here in their Sega guises:
- Sonic the Hedgehog
- Super Sonic
- Miles "Tails" Prower
- Knuckles the Echidna
- Amy Rose
- Cream the Rabbit and Cheese the Chao
- Rouge the Bat
- Espio the Chameleon
- Charmy Bee
- Vector the Crocodile
- Doctor Ivo Robotnik
- Metal Sonic
- Shadow the Hedgehog
- Silver the Hedgehog
Many Badniks from classic games make an appearance, such as Moto Bug, Buzz Bomber, Buzzer, Chopper, Crabmeat, Spiny, Grabber, EggRobo and Sandworm. The 3DS version adds Newtron, Crawl, Butterdroid, Dragonfly and Mushmeanie.
To date, there has not been an official adaptation of the game in Sonic the Comic Online. However, Tom Huxley "accidentally" wrote a script that heavily resembles the game. In Many Happy Returns, the Pirate Omni-Viewer brings a number of past and future versions of Sonic and Robotnik to the present in order to kill each other. When they realise what is going on, the current Sonic invites Vector and the Omni-Viewer along to put things right.
In Issue 257, a Review Zone was dedicated to Generations. Rather than have one reviewer comment on the game, four different people gave their opinions on the title. Although Stuart Gipp, Iain Stewart, Stuart Clack and Seumidh MacDonald each had their own individual take on the game, all four largely came to similar opinions. The title was left unrated.
The previous game in the series was Sonic Colours. The next is Sonic the Hedgehog 4: Episode II.