Robotnik's new weapon, Art, is the enforcer of Robotropolis new eradication policy. Art's objective is to destroy everything in sight, including Sonic, Manic and Sonia. The giant mechanical beast is seemingly unstoppable until he overhears the musical melodies of the Underground band.
Robotnik's new weapon, Art, is the enforcer of Robotropolis new eradication policy. Art's objective is to destroy everything in sight, including Sonic, Manic and Sonia. The giant mechanical beast is seemingly unstoppable until he overhears the musical melodies of the Underground band.
Manic, Sonic, Sonia must end their training early when Robotnik threatens the Oracle and takes a member of the resistance hostage. During the rescue mission, the Hedgehogs fall into trouble and begin to place blame upon each other for everything that has gone awry. Queen Aleena then intervenes with an important message for her children that they must learn to work together and derive strength from their willingness to help others.
Knuckles reluctantly makes a deal with Robotnik to turn over Sonic and his family in exchange for finding the Chaos Emerald that will save Mobius. Knuckles soon regrets that he ever trusted the evil dictator after Robotnik begins to follow through on his plans to roboticize the Hedgehogs.
The Hedgehogs begin to learn the important lessons of what it takes to be a freedom fighter. The Oracle provides teachers to guide Sonic, Manic and Sonia to develop the necessary skills to recognize the power that comes from within. The Hedgehogs also discover the hidden magical force of the power medallions as they grow to understand that teamwork will serve them best in averting the dangers that await them.
Sleet and Dingo escape the Flying Fortress with the Chaos Emerald. In a fight over who will control the Emerald's power, Sleet and Dingo drop and break the Emerald in two. Instantly, a rash of earthquakes and other natural disasters are sparked by the emerald's energy. Knuckles and the Hedgehogs turn to a relative of Knuckles for answers of how to stop Mobius from being slowly devoured by the emerald's force.
What is supposed to be a vacation for Sonic, Manic and Sonia turns into a battle to save Mobius when Robotnik attacks with his newest weapon - the Flying Fortress. Sonic investigates the ship thinking the weapon can be destroyed by removing its reactor, however his efforts fail and he goes to Knuckles for help, because he believes the weapon is powered by the Chaos Emerald.
The Hedgehogs latest quest to find their mother takes them to the prison tower where they encounter a masked stranger who insists he is family. This stranger is actually being used as bait for another attempt by Robotnik to capture them. The stranger creates a rift between the siblings, which leaves the Underground disbanded, vulnerable and ultimately trapped.
Sonic, Manic and Sonia find an abandoned baby in an alley and begin a search for the baby's parents. Manic grows particularly fond of the child and decides that instead of taking the baby to a shelter as Sonic and Sonia ordered, the baby would be more comfortable at the Underground sanctuary.
The Hedgehogs receive a message they believe is from their cousin. In the message, a castle is left to Sonia, who revels in the idea of having a castle for the Underground headquarters. Sonic, Manic and Sonia arrive at the castle only to see an old, dark dilapidated structure. Inside the castle, the Hedgehogs all have separate meetings with a mysterious apparition who resembles their mother.
Sonic, Sonia, and Manic are the children of Queen Aleena Hedgehog, the rightful ruler of Mobius, and are pursued relentlessly by Doctor Robotnik and his bumbling bounty hunters sidekicks, Sleet and Dingo. As infants, the siblings were separated and placed in hiding to fulfill a prophecy made by the Oracle of Delphius that the triplets would grow up to find their estranged mother, overthrow Robotnik, and take their places once more as Mobius' rightful rulers.