The citizens of a medieval-futuristic kingdom are protected by the Institute for Elite Knights, established by the legendary heroine Gloreth, who vanquished a "Great Black Monster" and enclosed the kingdom with a high wall one thousand years ago.

Ballister Boldheart is the first commoner to become a knight, as Queen Valerin is trying to change tradition so that "anyone can be a hero". During the ceremony, a laser shot from Ballister's sword kills Valerin. Ballister's boyfriend and fellow knight, Ambrosius Goldenloin, becomes distraught and disarms Ballister, dismembering Ballister's right arm in the process. Ballister becomes a fugitive.

As Ballister crafts a prosthetic replacement arm, he is visited by a shapeshifter named Nimona, who has faced persecution for her powers. Seeing a "villainous spirit" in Ballister, as he is facing similar treatment for his commoner origin and the murder of the Queen, Nimona declares herself to be his sidekick.