Act I: Don Pedro, King of Castile, has taken captive Constance, Princess of Navarre. She manages to escape from prison in disguise and takes refuge with Don Morillo, but she is recognised by the young Alamir. Alamir falls in love with Constance and rejects Don Morillo’s daughter Sanchette. The act ends with a divertissement in which warriors, gypsies and astrologers entertain the lords and ladies.