Isabel: Jewel of Castilla is a fictional diary of Isabella the first who reigned Castile (now Spain) in the 15th century. Isabel is the daughter of Juan II of Castilla and Isabel I of Portugal. Her father dies and her mother goes into a deep state of depression. Isabel’s brothers Enrique and Alfonso divide the kingdom, each proclaiming that they are the rightful king. They vie for control over Isabel, as they both want her to make a marriage alliance with anyone who they think can help defeat the other.The diary centers around the dilemmas that Isabel faces as she chooses which of her two brothers to support as king, and as she hopes to be married to someone who will not be completely repugnant to her. Isabel is forced to grapple with her conscience as she supports one of her brothers over the other in the struggle for the crown, and she poignantly must face her mother's growing madness that prevents her from recognizing her own children. Isabel displays great strength of will as she maneuvers from a position of weakness to broker a marriage that will not shackle her to someone she hates and fears. Courageously, she defies her brother in order to marry the prince she hopes she can love - a bright young man her equal in age and wit - and this gamble of hers ensures her legacy.