Antonio tries to learn more about the golden carp but Samuel is gone for the summer. Gabriel, meanwhile, is sad that his sons have left, and María is unhappy because her youngest brother Lucas is sick. They think a bruja cast a spell on him, and now he is about to die. Even the priest of El Puerto failed to cure him. Pedro Luna arrives and after much ceremony asks Ultima if she will come with him to heal Lucas.
Antonio is further disturbed by the knowledge that a priest failed to cure Lucas, and this knowledge increases his doubts about Christianity planted by the golden carp. The Lunas asked the Church for help first, as that is most socially acceptable and the Lunas are Catholics foremost, but they still respect Ultima's curanderismo enough to put their last hope in her.
Ultima agrees, but she reminds them of the consequences of tampering with fate. Pedro accepts responsibility. They say the curse is strong, but Ultima has powers she learned from her teacher, the flying man of Las Pasturas.
Ultima reminds them of the responsibility involved in passing judgment on someone, which relates to her advice about seeing and accepting all sides of an issue.
Pedro tells the story of the curse. Lucas entered an evil cottonwood forest at night, and there he saw the daughters of Tenorio Trementina dancing as fireballs and casting evil spells – performing the "Black Mass," a satanic ritual. Lucas stepped forward to denounce them and then saw who they were. They attacked him but he made a cross out of two sticks and drove them away, though the brujas cursed him as they fled. Since then he has grown deathly ill.
The novel truly becomes a piece of "magical realism" here, as the brujas' magic is condemned but still accepted as a reality of life. The Trementinas are introduced as antagonistic, vengeful characters, but Anaya only gives the Luna side of the story.
Ultima gathers her herbs and declares her readiness, looking small but dignified. She says Antonio must go with her. He is "a Juan" (his middle name) and has strong Luna blood. María protests but Ultima says it is the only way. She tells Antonio it will be hard and dangerous work, but he still agrees to come.
People named "Juan" were thought to be especially resistant to witchcraft. Antonio is revealed to be somehow necessary for Ultima's cure – he has a kind of magic inside himself as well. Ultima asks Antonio for his own decision, as she treats him like an adult.
They drive to El Puerto. On the way, they see an omen of the horned moon, which Ultima says is good luck for the Lunas as they live and farm by the cycles of the moon. They approach Prudencio's house, which is filled with women already dressed in black and mourning Lucas. Ultima tells everyone to leave and instructs Prudencio to prepare a room with food and water, and to not shoot the coyotes that will approach that night. She says she must speak to Tenorio first, and no one may come with her except Antonio.
Ultima has specific and strange instructions but Prudencio respects her powers enough to obey them without question. Ultima truly comes into her own here, and shows herself as a sure and forceful presence with her own strict code and set of ceremonies, which are totally different from the ways of the Church, but no less powerful.
They enter Tenorio's saloon, and at first he will not look at them. When he finally turns to Ultima his face is dark and cruel, and he makes the sign of the cross and calls Ultima a bruja. Ultima says she is a curandera come to undo his evil work, and she asks his daughters to undo their curse. She knows they gathered Lucas's freshly cut hair for their spell. Tenorio curses Ultima for accusing him and threatens to kill her, but cowers before her strength. Ultima says his daughters have tampered with destiny and so they must suffer the consequences. She and Antonio leave.
Tenorio appears as the antagonist of the novel, but his main quarrel with Ultima at first seems to be that he thinks she is a witch. Ultima shows her fairness in warning Tenorio what she is going to do and giving him the chance for repentance. Ultima acts as a balanced, forgiving presence similar to the Virgin of Guadalupe.
In the street they are caught in an ominous dust storm and Tenorio tries to run them over with his horse, but Ultima pulls Antonio aside just in time. The mourning women hurry away from the Luna house and Ultima enters at last. The house is quiet and empty. Lucas is on a bed looking like a corpse, but Ultima says there is still hope.
The image of the evil dust storm appears again, and is here associated with Tenorio's reckless rage. Antonio does not realize his danger, or fully understand the powers he has involved himself with.
Antonio wonders if Ultima can succeed where the Church failed. Ultima bathes Lucas and prepares an herbal remedy. They eat atole, which was a sacred food to the Indians. Antonio still does not feel afraid, and Ultima says it is because good is stronger than evil.
Ultima is a part of ancient rituals and indigenous ways. She has her own strong moral code, though it is more practical than dogmatic – Antonio does not need to be afraid because evil will not defeat them.
Coyotes howl outside the house but than Ultima's owl appears and attacks them. Antonio slips into a dream state and Ultima feeds Lucas more medicine. Antonio feels he is struggling with his uncle Lucas against the curse. Time dissolves into incense and the owl's hooting.
A supernatural process that is never explained, as the source of Ultima's powers and the world of her curanderismo remain mysterious to both Antonio and the reader. Antonio takes up the suffering of his uncle like a sort of priest.
Antonio wakes up and Ultima says they have defeated the death spirit, but the evil spirit remains. She makes another potion and then forms three clay dolls in the shape of women. Lucas breathes on the dolls and then Ultima sticks them with pins. Lucas drinks the potion and screams from the strength of it. Afterward Antonio falls asleep again.
The dolls add a suddenly sinister aspect to Ultima's magic – even she is not immune from the need to punish evildoers. The dolls are also associated with witchcraft, adding to the confusion between the powers of good and evil.
When he wakes up Ultima feeds Antonio more atole, and says Lucas has been almost healed. Antonio vomits and then feels better. Lucas sits up and screams, and then vomits out a writhing ball of hair. Ultima saves the hair and feeds Lucas, who is already looking better. She calls Prudencio inside and tells him that his son will survive.
Ultima succeeds where the Church and doctor failed, but her power remains unexplained and mysterious. The ball of hair adds to the tone of the supernatural and macabre.
Everyone enters the house rejoicing and thanking Ultima, but she tries to slip away. She says maybe the Lunas will save her life one day. People whisper about her as she leaves, but one of Antonio's aunts defends her from the word "bruja." Ultima makes Pedro drive her to the grove where the witches danced, and she disappears into the trees with the ball of hair. Antonio learns that he and Ultima were in Lucas's sickroom for three days. Ultima burns the hair in the grove where Lucas was first cursed. She returns to the truck, and Pedro praises her courage.
Even in her victory people still fear and condemn Ultima's power. The people she actually helps (now the Lunas, like María and Gabriel before) are able to appreciate and defend her, but those who do not understand Ultima's power will always remain prejudiced. She burns the hair to punish the Trementinas. Antonio returns to the "real" world, as he has been just as much a part of the magic as Ultima.