Origins: Sonic 3 & Knuckles - Part 1
After Sonic and Tails defeat Dr. Robotnik in Sonic the Hedgehog 2, Robotnik's space station, the Death Egg, crash-lands on the floating Angel Island. There, Robotnik meets Knuckles the Echidna, the last member of an ancient echidna civilization that once inhabited the island. Knuckles is the guardian of the Master Emerald, which grants the island its levitation power. Robotnik dupes Knuckles into believing Sonic is trying to steal the Master Emerald, turning the two against each other while he repairs the Death Egg.
Sonic and Tails approach Angel Island in their biplane, the Tornado. Sonic uses the Chaos Emeralds to transform into Super Sonic, but Knuckles ambushes him and steals the emeralds. Sonic and Tails travel the island hindered by Knuckles and Robotnik. At the Launch Base, where the Death Egg is under repair, Sonic and Tails fight Knuckles, but the Death Egg relaunches. On a platform attached to the Death Egg, they defeat Robotnik, causing the Death Egg to crash-land on Angel Island again. The story resumes in Sonic & Knuckles