When an undersea world is threatened by Captain Memo and his lobster sub, Sonic spreads a rumor that Memo plans to attack Robotnik next. When Robotnik hears of it, he launches an attack on Memo with a Shark-shaped sub, but Sonic's plan backfires when Robotnik decides that he will conquer the undersea world himself. With the help of a friendly school of porpoises, and the Mer-People of the undersea world, Sonic sends Robotnik and Memo floundering away.
Sonic the Hedgehog, the most fearless hero on Planet Mobius, uses his supersonic speed and teenage irreverence to thwart the comedically despicable Dr. Robotnik. Sonic’s idolizing little buddy, Tails, tags along on every fast-action, gag-driven adventure.