Kino, Juana, and their infant son, Coyotito, live in a modest brush house by the sea. One morning, calamity strikes when a scorpion stings Coyotito. Hoping to protect their son, Kino and Juana rush him to the doctor in town. When they arrive at the doctor’s gate, they are turned away because they are poor natives who cannot pay enough.
Later that same morning, Kino and Juana take their family canoe, an heirloom, out to the estuary to go diving for pearls. Juana makes a poultice for Coyotito’s wound, while Kino searches the sea bottom. Juana’s prayers for a large pearl are answered when Kino surfaces with the largest pearl either of them has ever seen. Kino lets out a triumphant yell at his good fortune, prompting the surrounding boats to circle in and examine the treasure.
In the afternoon, the whole neighborhood gathers at Kino’s brush house to celebrate his find. Kino names a list of things that he will secure for his family with his newfound wealth, including a church wedding and an education for his son. The neighbors marvel at Kino’s boldness and wonder if he is foolish or wise to harbor such ambitions.
Toward evening, the local priest visits Kino to bless him in his good fortune and to remind him of his place within the church. Shortly thereafter, the doctor arrives, explaining that he was out in the morning but has come now to cure Coyotito. He administers a powdered capsule and promises to return in an hour.
In the intervening period, Coyotito grows violently ill, and Kino decides to bury the pearl under the floor in a corner of the brush house. The doctor returns and feeds Coyotito a potion to quiet his spasms. When the doctor inquires about payment, Kino explains that soon he will sell his large pearl and inadvertently glances toward the corner where he has hidden the pearl. This mention of the pearl greatly intrigues the doctor, and Kino is left with an uneasy feeling.
Before going to bed, Kino reburies the pearl under his sleeping mat. That night, he is roused by an intruder digging around in the corner. A violent struggle ensues, and Kino’s efforts to chase away the criminal leave him bloodied. Terribly upset by this turn of events, Juana proposes that they abandon the pearl, which she considers an agent of evil.
The next morning, Kino and Juana make their way to town to sell the pearl. Juan Tomás, Kino’s brother, advises Kino to be wary of cheats. Indeed, all of the dealers conspire to bid low on the pearl. Kino indignantly refuses to accept their offers, resolving instead to take his pearl to the capital. That evening, as Kino and Juana prepare to leave, Juan Tomás cautions Kino against being overly proud, and Juana repeats her wish to be rid of the pearl. Kino silences her, explaining that he is a man and will take care of things.
In the middle of the night, Juana steals away with the pearl. Kino wakes as she leaves and pursues her, apprehending her just as she is poised to throw the pearl into the sea. He tackles her, takes the pearl back, and beats her violently, leaving her in a crumpled heap on the beach. As he returns to the brush house, a group of hostile men confronts him and tries to take the pearl from him. He fights the men off, killing one and causing the rest to flee, but drops the pearl in the process.
As Juana ascends from the shore to the brush house, she finds the pearl lying in the path. Just beyond, she sees Kino on the ground, next to the dead man. He bemoans the loss of the pearl, which she presents to him. Though Kino explains that he had no intention to kill, Juana insists that he will be labeled a murderer. They resolve to flee at once. Kino rushes back to the shore to prepare the canoe, while Juana returns home to gather Coyotito and their belongings.
Kino arrives at the shore and finds his canoe destroyed by vandals. When he climbs the hill, he sees a fire blazing, and realizes that his house has burned down. Desperate to find refuge, Kino, Juana and Coyotito duck into Juan Tomás’s house, where they hide out for the day. Relieved that the three did not perish in the blaze, as the rest of the neighborhood believes, Juan Tomás and his wife, Apolonia, reluctantly agree to keep Kino and Juana’s secret and provide shelter for them while pretending to be ignorant of their whereabouts.
At nightfall, Kino, Juana, and Coyotito set out for the capital. Skirting the town, they travel north until sunrise and then take covert shelter by the roadside. They sleep for most of the day and are preparing to set out again when Kino discovers that three trackers are following them. After hesitating briefly, Kino decides that they must hurry up the mountain, in hopes of eluding the trackers. A breathless ascent brings them to a water source, where they rest and take shelter in a nearby cave. Kino attempts to mislead the trackers by creating a false trail up the mountain. Kino, Juana, and Coyotito then hide in the cave and wait for an opportunity to escape back down the mountain.
The trackers are slow in their pursuit and finally arrive at the watering hole at dusk. They make camp nearby, and two of the trackers sleep while the third stands watch. Kino decides that he must attempt to attack them before the late moon rises. He strips naked to avoid being seen and sneaks up to striking distance. Just as Kino prepares to attack, Coyotito lets out a cry, waking the sleepers. When one of them fires his rifle in the direction of the cry, Kino makes his move, killing the trackers in a violent fury. In the aftermath, Kino slowly realizes that the rifle shot struck and killed his son in the cave.
The next day, Kino and Juana make their way back through town and the outlying brush houses. Juana carries her dead son slung over her shoulder. They walk all the way to the sea, as onlookers watch in silent fascination. At the shore, Kino pulls the pearl out of his clothing and takes one last, hard look at it. Then, with all his might, under a setting sun, he flings the pearl back into the sea.