The novel is about the different paths one may take in life. In particular, it's about the dichotomy between righteousness and evil. The two girls at the center of the story—Manuela and Pilar—are godsisters, but it is evident from the beginning of the story that they are polar opposites in terms of personality and ambitions. Manuela is someone who is bored with her simple life, while Pilar represents a principled and down-to-earth woman.

Manuela is a complex character, however, as she does have a moral compass. This can be seen in a later section of the book, in which she feels sympathy for a French captive being tortured by the bandits. In the end, Manuela chooses to live and die by the gun.

In the beginning of the story, the two young women joke about marriage. Manuela teases Pilar about putting flowers representing marriage in her hair. Manuela sees Pilar as a simple girl; someone who Manuela does not want to become. However, later on in the novel, Manuela feels a sense of jealousy (although not malicious jealousy) toward Pilar when she sees the floral arrangement in her hair. Manuela sees that it was Pilar who chose the good life by marrying a decent man, Nicolás.

Though El Zarco is named in the title, he is merely a secondary character, a caricature of an evil person. The true character studies in the story are Manuela and Pilar. El Zarco and Nicolás are merely the male counterparts of the female characters. Nicolás is simply a reflection of Pilar. El Zarco, however, is not a carbon copy of Manuela. As stated earlier, Manuela does show humanity; El Zarco is completely ruthless toward the people he terrorizes.

El Zarco is a representation of the life Manuela thought she wanted to live back when she was still young and naive. After reality sets in, it is already too late for Manuela to leave the life she chose, and she dies soon after her terrorist lover is executed by a militia.