After vanquishing Dr. Robotnik, Sonic grows restless on South Island and embarks on a new adventure, only to return and discover his world eerily emptied of inhabitants. His search for answers leads him to witness his young companion Tails being seized by the villainous Dr. Robotnik, who demands six Chaos Emeralds as ransom for the fox's release. With Tails imprisoned in the mysterious Crystal Egg and a half-dozen powerful mechanical guardians standing between him and his goal, Sonic must race across the island to collect the emeralds and mount a daring rescue before it's too late.