In a medieval dungeon, a prince has been imprisoned for more than twenty years for an alleged crime. His testimony supports some fantastic facts, which is why he is identified as a person possessed by the devil or insane. A sorcerer, spokesman for the King, visits him periodically to achieve his improvement, so that the prince is released and is in a position to become the future king. The prince is not willing to deny what he saw. But the sorcerer offers him a deal that puts the values, truth and justice of the entire kingdom at stake. Príncipe Constante reveals the true story behind a lie that accompanied us from our childhood until today. But now the truth is known.