Isabel and her brother Alfonso live happily in Arévalo with their mother Isabel of Portugal, widow of King Juan II of Castile, along with her tutor Juan Chacón and his wife, Beatriz of Bobadilla. However, one bad day they are forcibly taken to the court of Segovia by order of their stepbrother, King Enrique IV, on the occasion of the pregnancy of his wife, Mrs. Juana of Avis. Isabel and Alfonso remain under the care of the queen, who despises and fears them at the same time because they constitute a threat to the future of the daughter she is waiting for.