A wizard named Merlina, granddaughter of Merlin, running away from some pursuer, summons Sonic to help free the mystical realm of King Arthur, who has been possessed by an unknown evil that comes from Excalibur's scabbard, and is now ruling the realm as the tyrannical Black Knight. Sonic's speed alone will not end the Black Knight's reign, so he must take up the talking sword, Caliburn and master swordsmanship in order to break Arthur's curse and save the kingdom.