The game features Sonic the Hedgehog as the only playable character, although night-time sees him transform into the bulky Werehog form, thanks to the machinations of Doctor Robotnik. The scientist also uses the power of the Chaos Emeralds to tear apart the planet, scattering the continents and prematurely freeing Dark Gaia. Along with new friend "Chip", Sonic sets off on a quest to restore power to the drained Chaos Emeralds, rejoin the planet and defeat two deadly foes.