After the events of a previous adventure, Sonic and Tails detect a powerful energy signal on Angel Island and fly out to investigate. Dr. Eggman's elite robots, the EggRobos, reach the source first, a magical gemstone called the Phantom Ruby, and are transformed by its power into the Hard-Boiled Heavies. The gem warps Sonic, Tails, and the island's guardian Knuckles across familiar territories as they race to stop Eggman from harnessing the ruby's reality-bending abilities. With the Hard-Boiled Heavies pursuing their own ambitions and Eggman scheming to use the Phantom Ruby to retake control of Little Planet, the trio must chase the doctor through zone after zone before his plans can be realized.