It's the mid-11th Century. Ruy es 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 is wants the man who upset the conspiracy. Rodrigo knows it was his grandson, which is why he intends to send him off to Vivar. On the other hand, Ruy resists leaving the King at the expense of Flaín, as he sees the only solution being to end 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 tohug him. Fernando starts to investigate who betrayed him. Meanwhile, Ruy leaves León ignorant to the fact Flaín sent a hitman within the troop tohug him.

The Castile troops 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.

After Fernando's subsequent illness, Sancho and his troops return to León. Ruy tells his grandfather that Flaín sent someone tohug 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 passing. He is unaware that Urraca still has a card to play.