Dr. Eggman (aka Dr. Robotnik) is back to continue his zealous search for the Chaos Emeralds needed to fuel his new Death Egg contraption. The evil doctor secretly follows Sonic to his vacation spot, Westside Island, and launches a full-scale attack, imprisoning all the helpless animals of the island and turning them into mindless worker drones. Now Sonic must thwart the doctor's plans at all costs. This time he isn't alone, as a peculiar two-tailed fox named Miles Prower (aka Tails) decides to aid him in the battle. Together they must locate the Chaos Emeralds before Dr. Eggman does, and put an end to his diabolical scheme.