The two main characters are two brothers; the older Jonatan and the younger Karl. The two brothers' surname was originally Lion, but they are generally known as Lionheart. Karl's nickname is Skorpan (Rusky) since Jonatan likes these typical Swedish toasts or crusts.
In Nangijala, a land in "the campfires and storytelling days", the brothers experience adventures. Together with a resistance group they lead the struggle against the evil Tengil, who rules with the aid of the fearsome fire-breathing dragon, Katla.