Sonic and Tails are flying in Sonic's biplane, looking for Dr. Robotnik's hovercraft, when they see an island floating in the sky. Curious about what keeps the island afloat, they decide to check it out. However, a mysterious figure shoots a rocket at their plane. Tails saves Sonic using his flying powers and they land on the island unharmed. Sonic suspects Robotnik is behind this and looks for natives, hoping to ask for help. An Assaulting Batter Blimp attacks them, and Sonic and Tails retreat into a nearby pool of water. They end up in an underwater maze filled with spikes and traps and are sucked into a giant drain. Sonic and Tails lose consciousness, and wake up to find themselves tied up in a dark room. It turns out Knuckles the Echidna is their captor. Knuckles tells them that his "pal", Dr. Robotnik, informed him that Sonic and Tails would come to steal the Chaos Emerald that keeps his island afloat.
