Kino, Juana and their infant son Coyotito live in a modest brush house by the sea. One morning, calamity visits their home when Coyotito is bitten by a scorpion. With hopes of protecting their son, Kino and Juana rush him to the doctor’s clinic in town. However, when they arrive at the gate, they are turned away because they are poor natives and not paying customers. Later that same morning, Kino and Juana take their family canoe out to the estuary to go diving for pearls. Juana makes a poultice for Coyotito’s wound while Kino canvases 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, wondering if he is wise or foolish to hold such ambitions. Toward evening, the local priest visits Kino, to bless him on his new fortune, and to remind him of his place within the church. Shortly after, 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 this period, Coyotito grows violently ill and Kino decides to bury the pearl under the floor in a corner of the brush house. After the doctor returns, he feeds Coyotito a potion to quiet the baby’s spasms. When the doctor inquires about payment, Kino explains the story of the pearl to him. This intrigue tands watch. Kino decides that he must attempt to attack them unawares before the late moon rises. He strips naked and sneaks up to striking distance. Just as he is prepared to pounce on them, 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 flurry. In the aftermath, Kino slowly realizes that the shot has 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 with her dead son slung over her shoulder. They walk all the way to the sea, with onlookers watching in silent fascination the whole while. At the shore, Kino pulls the pearl out from his clothing and takes a last hard look at it. And then, with all his might, under a setting sun, he flings the pearl back into the sea .