Tails' latest plane is missing, but this one's got a tracking device - leading Sonic and Tales on a frantic flight to the Mystic Ruins. When they get there, they not only find both Robotnik and Knuckles, but a threat they hoped they'd never have to face again. Back in the city, all seems tranquil for the Mayor and Sally, but you know that can't last - and before you know it, Sonic, Tails and Knuckles are back to try to restore order. What is the mystery that threatens their very existence? Will a cocky hedgehog, a headstrong echidna and an eager fox be enough to save civilization?