 Sonic was trying to relax after he fought Chaos in Sonic Adventure 2, however he got captured by the military being accused of his "crimes. " It turned out that a look-alike, Shadow the Hedgehog, was behind the whole mess. As Robotnik is still concocting a plan to conquer Earth (again!), Shadow is more than willing to help him. Meanwhile, Tails, and Amy try to find out why Sonic is framed. Knuckles, on the other hand, has to recover shards of the Master Emerald since he and his rival, Rouge the Bat, accidentally broke it into pieces. Rouge the Bat, is also going undercover to find out Robotnik s plans while pretending to side with Robotnik. Shadow partially reveals secrets about a weapon on a space colony, ARK. Shadow was created by Robotnik s great-grandfather, Dr. Gerard Robotnik. He is ageless and immortal. 50 years ago in Shadow s time, the military shot Gerard s granddaughter, Maria, while trying to escape. Since Shadow swore to take revenge on all of the people living on Earth, he assists Robotnik s plans in getting 7 Chaos Emeralds. They are required to power up the "secret weapon. " Now it is up to Sonic, Tails, and Knuckles to stop Robotnik s plans. Save the world as the Good Guys, or rule the world as the bad guys!