A new character, Knuckles the Echidna, is guardian of a very special Emerald. This is called the Master Emerald. It is even more precious and powerful than all of the seven Chaos Emeralds. The Master Emerald is situated on the Floating Island. Knuckles guards this precious emerald. Robotnik believes that the Master Emerald could power his Death Egg forever! He tricks Knuckles into letting Robotnik on his side, and therefore have access to the Master Emerald. Knuckles is in turn fooled into thinking that Sonic and Tails are bad guys! As Sonic and Tails reach Angel Island, Knuckles nicks off with all of Sonic's Chaos Emeralds. It's up to Sonic to save the day.