Diego Alatriste is a soldier in the service of King Philip IV of Spain during the Eighty Years' War.

Alatriste is hired along with a Sicilian assassin named Gualterio Malatesta to kill the Prince of Wales (the future King Charles I of England) and his companion, the Duke of Buckingham.

The duel with his friend Martín Saldaña and the punishment of Íñigo in the galleys are part of the film's spectacular ending.

During the battle, Abel Moreno Gómez's "La Madrugá" is playing as the defeated army's march and this is where it is assumed that Alatriste dies.

The plot of the film has elements from each of the five books published up to the premiere, and it maintains the same storyline for the main characters.