Robotnik severely upsets the ecosystem above and below the surface, when he sends explosive, Robotnik snake probes drilling deep underground in search of oil lakes. After being swept into an underground world by a whirlpool, Sonic, Sally, Antoine, and Robot discover a strange creature who claims he is the last of a people who have been destroyed by surface creatures and blames the Freedom Fighters for his plight. Robot gets a chance to become a hero for a change, when he saves Sonic and the others from a toxic pot of technojunk, but it's up to the Hedgehog to turn the tables on Robotnik and destroy his drilling platform and team of lethal snake probes.