The Hedgehogs steal historical artifacts of Mobuis from Robotnik before he can pawn them off at an auction. Sonic and Sonia take one of the pieces to a university professor who informs them that the artifact is actually a bomb from the Mobian war. The Hedgehogs must act fast to retrieve the bomb and protect the treasure that is the key to Mobius past.

As Sonic begins to chow chili dogs for a snack, he finds a message in the sack from his mother urging him to head to Speedster Island. When he, his brother and his sister arrive, what they encounter is an ancient sanctuary that is about to be overrun by Robotnik and sold off bit by bit. The Hedgehogs must persuade Bartleby to end his deal to build a resort on the beautiful island and save the people of the village from becoming slaves of Robotnik.