Diego Alatriste is a soldier in the service of King Felipe IV, during the Eighty Years War.

The story begins in the Netherlands, where the tercio of Diego Alatriste fights against the Dutch. Lope Balboa (father of Íñigo and friend of the captain) is killed here. Diego decides to return to Madrid where he receives the young Íñigo Balboa in his care. He is hired, along with a Neapolitan assassin named Gualterio Malatesta to kill the Prince of Wales (future King Charles I of England) and his companion, the Duke of Buckingham. The job is contracted by Emilio Bocanegra and Luis de Alquézar (uncle of Íñigo's love interest - Angelica de Alquézar). Alatriste finally returns to the Netherlands in 1624 (although the movie says it's 1625) and participates in the final battles leading to Breda's surrender. After the return to Spain, Íñigo wants to elope with Angelica, but she gets cold feet at the last moment. Alatriste has a romance with actress Maria de Castro, who was the lover of Philip IV and he ends up crossing his sword with Gualdamedina, a friend of the king. In the end, the object of their attention gets sick with syphilis. The duel with his friend Martin Saldaña and the punishment of Íñigo in the galleys are part of the film's spectacular ending. The last scenes are at the Battle of Rocroi (May 1643), described in the last book of the long and entertaining saga The Adventures of Captain Alatriste, a book that has not been published as of 2008. 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 the old Captain Diego Alatriste dies.