It’s the mid-11th Century. Ruy is a young man who has just been named squire to Prince Sancho, King Fernando of León’s eldest son. One night he discovers that someone he loves is involved in a conspiracy to overthrow the King. From then on, Ruy is caught between his loyalty to duty and to his heart.

Flaín wants to find the man who frustrated the conspiracy. Rodrigo knows it was his grandson, which is why he intends to send him off to Vivar. However, Ruy resists leaving the King at the mercy of Flaín, and he thinks that the only solution is ending the Count of León's life. When it looks like everything is about to kick off, the Navarre troops turn up at the border and declare war against León.

Fernando sends his son, Sancho, with a small army to Zaragoza to confront his brother, Ramiro, the King of Aragon. Before leaving with Sancho, Ruy reveals to the King that Flaín tried to kill him. Fernando starts to investigate who betrayed him. Meanwhile, Ruy leaves León ignorant to the fact Flaín sent a hitman within the troop to kill him.

The Castile tropos with Sancho and Ruy fight an outnumbered battle against the Aragonese. When all seems lost, the outcome seems totally unexpected. In León, Fernando discovered who was conspiring against him, among whom his wife, Sancha. Unbeknownst to the King, his daughter, Urraca, has also made a decision that will change the power balance forever.

After Fernando’s subsequent illness, Sancho and his troops return to León. Ruy tells his grandfather that Flaín sent someone to kill him. Rodrigo knows his grandson’s life is in danger. Flaín, on the other hand, doesn’t give up on his mission to conspire against the dying King and decides to attempt seizing power before his death. He is unaware that Urraca still has a card to play.