After the events of Sonic 3 & Knuckles, Dr. Eggman managed to get the pink Chaos Emerald and enhances it with his machine, his machine is destroyed, but the Emerald becomes one of the most powerful gems in the Earth, and Dr. Eggman uses it to power Death Egg. Meanwhile on Green Hill, Sonic and Tails notice that the Death Egg has risen from the mountains. They hop on the Tornado, and begin their adventure to stop Dr. Eggman.