A wizard named Merlina, granddaughter of the original Merlin, 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, in order to break Arthur's curse and save the kingdom. Sonic must also collect the blades of King Arthur's Knights of the Round Table and Excalibur itself if he is to restore King Arthur's sanity and return him to a benevolent ruler. Sonic is assisted in his travels by a kind blacksmith and the legendary Lady of the Lake. Facing dragons, King Arthur's warriors from the Underworld and the Knights of the Round Table (who bear similarities to Shadow the Hedgehog, Knuckles the Echidna, and Blaze the Cat), Sonic collects the blades and enters a showdown against the Black Knight. However, when the dust settles, it is revealed that King Arthur was merely an illusion, and that Merlina was using Sonic so that she could become all-powerful and make the kingdom last forever. Sonic fights her, but takes a severe beating the first time and Caliburn is destroyed. Sonic's resolve to stop her, however, is great, and with this resolve (as well as the Knights' blades), Caliburn is restored and revealed to be the true Excalibur and Sonic is turned into Excalibur-Sonic (a variation of Super Sonic). With their new power, they fight Merlina (who has become the Dark Queen) and convince her that, although her world may be ending, she needs to live life to the fullest. With the fight over, the Knights of the Round Table are about to disband (due to King Arthur's death), but Caliburn says that he is the one who chooses the king, who is Sonic (since only the true king could have pulled Excalibur from the stone). After the credits, Sonic tries to tell Amy of his adventure, but she thinks he missed her date on purpose. The game ends in a fashion similar to Sonic and the Secret Rings, with the book "King Arthur and the Knights of the Round Table" changing to "Sonic and the Black Knight".