Teodoro Golfín, a renowned eye surgeon, has just arrived at the fictional town of Villamojada in Northern Spain in search of the mines of Socrates. At the request of the wealthy Francisco Penáguilas, Teodoro has come to attempt to cure his son, Pablo, of his blindness. On his way to the mines, Teodoro gets lost. He is aided by the arrival of Pablo, who offers to lead Teodoro to the mines where the doctor can find his engineer brother, Cárlos and his wife, Sofía. Along the way, Teodoro meets Nela, a young girl who serves as Pablo’s companion as she is too weak for any other labor in the mines.  

When Pablo learns from his father that Teodoro may cure him of his blindness, he becomes obsessed with the idea of beauty. Pablo asks if Nela is beautiful, believing that she might be because of her goodness of spirit. Nela is fearful that once Pablo sees her at long last, he will find her ugly and discard her. He reassures her otherwise.

Meanwhile, Teodoro learns about Nela’s family history, including the suicide of the young girl’s mother when she jumped into La Trascava. Teodoro expresses sympathy for Nela’s family whereas the people around him, including Sofía, can only muster judgment. When Nela injures herself to rescue Sofía’s dog, Teodoro shows his kindness by taking the thorn from her foot, bandaging it, and carrying her home on his shoulders. Along the way, he shares the story of his and Cárlos’ rise from poverty. As youth, they worked hard in Madrid to make a living to support their respective studies. They each fared well enough to become highly skilled in their respective fields of anatomy and mathematics. Nela returns to the Centeno house to tell Celipin of the story of Teodoro and Cárlos’ rise to success. Celipin aspires to be a doctor like Teodoro. He invites Nela to run away with him, but she declines. He tells her that once Pablo gains his sight, there will be no need for her as the young boy’s guide. This news brings Nela tremendous sadness. That night, she dreams of the Virgin Mary. 

The next day, possessed by images of the Holy Mother, Nela believes that she has encountered the divine figure in the form of Florentina, Pablo’s cousin, who has arrived with her father, Manuel. Manuel and Francisco plan for their children, Florentina and Pablo, to marry, in order to collect interest on an inheritance from a recently deceased family member. When Nela hears of this plan, she is heartbroken as she knows that she can never compare to Florentina in beauty or status.

Florentina proves to be kind and charitable, which makes it difficult for Nela to sustain resentment towards her. Her compassionate spirit moves Pablo too. Before Nela, Florentina makes a vow to the Virgin Mary to educate the young orphan and care for her as if she is her own sister, should Pablo’s surgery be a success. When Pablo’s surgery does prove to be a success days later, Nela attributes the positive results to Florentina’s divine intervention. In the days after Pablo’s surgery, Nela hides from Pablo despite his repeated demands to see her. During her time of hiding, Nela makes plans to run away with Celipin. 

On the day of their anticipated departure from Socrates, Nela encounters Florentina who has come in search of the young orphan. Florentina demands to know why Nela has not visited Pablo, but Nela can only respond in tears. Not understanding the true reasons behind Nela’s upset, Florentina attempts to guide Nela to Pablo’s house despite the orphan’s grievous cries. Suddenly, Nela runs away from Florentina. She runs into Celipin who is on his way out of Socrates. He implores Nela to leave with him once more, but she declines, as she believes she will be a burden to him. As they part ways, Nela hides from Teodoro who has learned of her escape from Florentina. When Teodoro finds Nela, he demands to know the truth behind Nela’s behavior. Nela confesses her love of Pablo and her fear of his sight of her. She desires to end her life and to join her mother in the La Trascava abyss. Teodoro takes pity on her and reassures her that all will be well if she goes with him. Eventually, Nela relents and allows Teodoro to carry her to Pablo’s house.

At Pablo’s house, Nela sleeps in Florentina’s room. Teodoro and Florentina discuss Nela’s future, and it appears briefly that Nela may prefer to go with Teodoro. Suddenly, Pablo enters Florentina’s room, demanding to know where his cousin has been. He sees Nela in bed and mistakes her for a random charitable case under Florentina’s care. When Nela reveals herself to Pablo, he can only look on in shock and silence. His reaction causes Nela to die from grief.