The game takes place on Emerald Island, which is a convex island, hidden underneath Angel Island. Legends say that the Island is the origin of the Echidna Tribe, the Master Emerald and the Chaos Emeralds; it also possesses other powerful gems. Robotnik detects an energy source from this Island and obtains the Discord Stone and harnesses its power into his newest machine: The Steampunk Egg. Sonic and Tails catch wind of his plans and decide to go and stop his nefarious plans before he gets a chance to destroy the whole planet!