The centaur Biron is accidentally transformed into a horse by a grateful Circe (she meant to make him human) and given superpowers to make up for the mistake; confined on an asteroid by an evil magican, he is eventually freed by Kara Zor-El's rocket and follows her to Earth where he eventually unites with Kara, who has grown up to be Supergirl, to fight evil as Comet the superhorse.