Dr. Ivo Robotnik is back and has released Chaos Zero from the Master Emerald. Chaos Zero watches over the Master Emerald Shrine on Angel Island. Now he wants to use Chaos Zero to destroy Station Square and build "Robotnikland". Chaos can grow stronger with every Chaos Emerald he "eats". When he gets all 7, it's all over... but not while Sonic's around. Along with Tails, Amy, Knuckles, and new characters E-102 Gamma and Big The Cat, Sonic must save Station Square in his hugest adventure yet.