When Queen Juana is finally pregnant after 7 years of marriage, King Enrique IV orders that his half-siblings Isabel and Alfonso be brought from their home in Arevalo to the decadent Royal Court of Castile in Segovia.

Lead by Marquis Juan Pacheco and Archbishop Carrillo, several nobles rebel against the King under trumped-up charges. Enrique's supporters extort him to act, but he is unwilling to display violence.

Beatriz is shocked to learn that her father has given her hand in marriage without even consulting her. Meanwhile, the King decides to use another wedding to end the country's civil war: Isabel's.

The civil war in Castile comes to its most decisive point as the armies of Enrique and Alfonso face each other in Olmedo. In Segovia, the Queen prays for her husband and Isabel for her younger brother.

After their recent loss, Carrillo advices Isabel to continue the war and Chacón to seek peace. Enrique finds betrayal in a place he didn't expect. Chacón worries as Gonzalo and Isabel compare their feelings for each other.

Isabel and Enrique debate peace terms at Guisando. King Juan II of Aragon, seeking Castilian support against France, sends his emissary Peralta to negotiate the marriage of his heir Fernando - to Juan Pacheco's daughter.

Isabel debates her marriage options. Her supporters want her to marry Fernando, and Enrique, the King of France's brother. Pacheco and the King count as an advantage that the devout princess won't lie to them.

Fernando travels under disguise to meet Isabel in Valladolid, keeping an eye out for bandits and Pacheco's men. Isabel grows afraid as the time to sleep in the wedding bed comes near. Gonzalo can't hide his jealousy.

Isabel and Fernando marry in Valladolid with the support of several nobles and are acclaimed by the people. However they are cousins and the marriage needs a Papal bull to be valid.

Hearing good news from Rome, Enrique makes his new move by blockading Valladolid. With no food for the winter, the people's support for Isabel and Fernando vanishes. Fernando also grows sick of Carrillo's meddling.

Isabel and Fernando find refuge in Medina de Rioseco but their situation is dire. Pacheco's army is on the move, ready to punish their supporters. Fernando suspects of Carrillo, while news of her husband's infidelity drive Isabel mad.

King Juan convinces the new Pope to sign the bull authorizing Isabel and Fernando's marriage. Rome's envoy, Cardinal Borgia, also must propose a new Castilian cardinal - a position that Carrillo and Pedro Mendoza strive for.

Cabrera convinces the King to receive Isabel and Fernando in Segovia. Away from the Court, Pacheco offers Queen Juana his support while he plots to kidnap Isabel and her daughter.

Isabel's decision to take the Crown while Fernando is in Aragon angers him, a division that Carrillo is eager to use. Meanwhile, Diego Pacheco seeks support from Portugal and the nobles to dethrone Isabel in favor of Juana.

Reconciled, Fernando and a pregnant Isabel face their biggest test yet as the Portuguese invade Castile. King Alfonso marries Juana to reinforce her claim, but is reluctant to consummate the marriage as his supporters insist him to.

Fernando besieges Burgos while the Portuguese try to send a relief column to the rebels. Meanwhile, Isabel balances the conflicting interests of the Aristocracy, the Church and the Jews to finance the war.

Isabel debates showing mercy to the rebels when the new bread tax causes an uprising in Segovia. Chacón ponders retirement. Juana feels imprisoned during her husband's absence and seeks solace in her stepson, the Prince of Portugal.

Isabel visits Seville, Castile's richest city but also a place plagued by crime and corruption. Juan II accuses Fernando of caring more for his wife's kingdom than for his. A border incident sours relations between Castile and Granada.

The King's long absence throws Portugal in confusion, but Isabel and Fernando are no less divided over their next move. Rome pressures Castile to adopt the Inquisition. In Granada, the jealous Aixa plots against the Emir.

The converts of Seville look at their options in the face of the Inquisition. Juana's unruliness threatens the peace between Portugal and Castile. Beatriz learns her nephew's secret. Muley-Hacén names his heir.

It's time to visit Aragon to nominate Prince Juan as heir to the kingdom, but this is the least of Isabel and Fernando's problems. Granada invades Zahara, Catalonia is divided and the royals must face their most dangerous pregnancy yet.

The war bogs down as the nobles of Spain prefer to pursue their own interests before the Crown's, but a stroke of luck might tip the balance in the fight between Christians and Muslims. In Portugal, the king seeks to reinforce his position.

Fernando makes his authority in Aragon clear. Isabel receives a foreign sailor with a bold proposal. El Zagal rallies all Muslims to make common front against the Christians.

Fernando lays siege to Malaga, El Zagal's stronghold and richest city in Granada, while the Muslims appeal to their brethren outside Europe. Isabel receives the two queens of Granada.

Just as the Granada War nears its end, Prince Juan's sudden illness threatens to give Isabel and Fernando's kingdoms to the Portuguese. Columbus retouches his plan, and Torquemada investigates a murder.

The ultimatum to Boabdil expires. Isabel and Fernando decide on the future of Granada, the Jews, the dispute with France and Columbus' enterprise.

Columbus' voyage is a success but a storm forces him to land on Portugal. The royals travel to Barcelona to sign a treaty with France, who ambitions to conquer Naples. The queen meets her new confessor, and her daughter ponders her future.

Columbus hides his doubts as he is pressed to make a second voyage. Portugal disputes the new lands to Castile, and France invades Italy. In Rome, the Pope juggles the rival countries interests for his own benefit.