Doctor Robotnik searches for a new way to crush his old rival Sonic and seize control of the world. His research leads him to Chaos — a being that, thousands of years ago, protected the Chao and the all-powerful Master Emerald, which holds the seven Chaos Emeralds in balance. When a tribe of echidnas tried to steal the Emeralds' power and shattered their harmony with the Chao, Chaos used that power to become the monstrous Perfect Chaos and wiped them out. Before the world could be destroyed, Tikal, a young echidna who had befriended Chaos, sealed it — and herself — within the Master Emerald. Now Eggman releases Chaos, and Sonic and his friends must thwart his scheme and keep the creature from growing more powerful.