Three months ago, Sonic and his friends defeated Silver Sonic II and reprogrammed it to chase Dr. Eggman out of Station Square. The robotic guardian chased him all the way to Prison Island, where the doctor fell into a deep crevasse, supposedly to his death. Eggman found himself in an abandoned, high tech jail cell that had previously held his grandfather. Inside, he found the professor's secret journal, revealing to him a secret weapon.