"Les Mystérieuses Cités d'Or" follows the adventures of Esteban, a young Spanish conquistador, who embarks on a journey to find the legendary Cities of Gold, hidden somewhere in the New World. Along the way, he meets a mysterious girl named Zia, who possesses a golden pendant with magical powers. Together, they encounter various cultures, mythical creatures, and hidden treasures, while navigating treacherous landscapes and rival expeditions.