At Aleena's Kingdom,She shows Sonic,Sonia,and Manic the Blue Chaos Emerald. The Keepers has each emeralds. The Hedgehogs meets with the Keeper of the Emeralds,Pachacamac the Echidna Chief,Razor the Shark of the Sol Empire,Monkey Khan,Prince of the Dragon Kingdom,Lupe,Chief of the Wolf Pack,and Elias Acorn,the future king of the Acorn Kingdom.
While celebrating,Sonic meets with Elias' sister,Sally,who has been Sonic's childhood friend. Sonia was smitten with Khan. The Celebration was interrupted by Robotnik and his robots. He tries to battle him,but is confronted by Knuckles.
The Robots open fire,killing Pachacamac,capturing Razor,Khan,Sally,Lupe,Sonia,and Manic,and taking the Six Emeralds. Knuckles was about to take Sonic down,but was saved by Amy Rose,who has crush on Sonic since his heroism. The heroes quickly escape.
Pachacamac's Daughter,Tikal reveals that Knuckles is his Childhood Friend,but he became an outcast to the clan. She shows them the mural of the Emeralds and there's a Seventh Emerald hidden somewhere. She reveals that the Seven Chaos were once one called the Master Emerald,but it was broken into Seven.
Believing that someone could use it turn thoughts into reality,One of them is hidden while the six kept each of them.
Sonic goes on the journey with Tails,Amy,Rotor,and Antoine. Robotnik learns about the Emeralds and begun searching for the Seventh. Sonic and his group arrive at the Mountains where the seventh emerald is hidden. They are later confronted by Robotnik and Knuckles. Sonic begun battling with Knuckles,who reveals that he was an outcast because he has gotten his fellow members killed while facing the enemy who killed his father.
Robotnik has put the emeralds together and betrayed Knuckles. He uses the Master Emerald to create the Death Egg Robot. Tails and Amy manage to save the captives. Tikal comforts Knuckles,telling him not to give up hope. He joined Sonic,Tails,and Amy to fight against Robotnik. They manage to separate him from the Emeralds. Sonic,Sonia,and Manic manage to reach the Emeralds,
transforming into Super Hedgehogs to defeat Robotnik,destroying the robot.
Robotnik disappears through the smoke.
After Knuckles puts the Emeralds back together,the Heroes are praised by the people. Sally and Amy begun competing on who wants Sonic. Knuckles must go to meet with his guys,but he'll be in touch with Sonic's group.
Mid-Credits:
Robotnik,who survived the fall,meets with his Nephew,Snively. He shows him one of Sonic's quills that he found.