While Kino, a pearl diver, and his wife, Juana, eat breakfast, a scorpion stings their infant son, Coyotito. Juana tries to suck the venom out of the baby's wound, then takes him to the village doctor. Kino talks to a servant, who, after speaking to the rich doctor and showing him some pearls Kino offers as payment, returns the pearls and says the doctor had to attend a serious case. Kino is furious and ashamed.
On the beach, Juana rests Coyotito in Kino's canoe, covers his wound, and, with Kino, paddles to the nearest oyster bed. There, Kino dives and finds the biggest pearl they have ever seen. Juana shrieks as she notices Coyotito's wound has improved in the presence of the pearl, and other canoes gather around to find out what happened.
Everyone comes to Kino and Juana's house to admire the pearl, and Kino shares his plans now that he has a fortune. After the doctor visits and medicates Coyotito, Kino buries the pearl in a corner. Coyotito becomes sicker, but the doctor returns, soothes him, asks for payment, and offers to keep the big pearl in his safe, making Kino inadvertently look toward the buried pearl. Later, Kino reburies the pearl under their mat and sleeps on it with his family. He wakes to an intruder scratching the first place where the pearl was buried, and stabs him. Juana says the pearl is evil, but Kino insists it is their salvation.
When Kino tries to sell the pearl, the dealers either lowball or reject the pearl, so Kino announces he is selling the pearl in the capital. That night when a man approaches their doorway, Kino fights him but is wounded in the struggle. Juana begs him to discard the evil pearl, but Kino insists on leaving for the capital in their canoe next morning.
Kino sees Juana sneak out with the pearl, beats Juana down, and leaves her on the beach. On his way back, Kino is assaulted by a group and kills a man. As Juana gets up, she finds the pearl and sees Kino and the dead man lying on the road. She hides the corpse, convinces Kino to flee, and rushes home to fetch Coyotito. Kino finds someone has made a hole in his canoe and set their house on fire. The family quietly heads north.
Kino tries to read the future on the pearl and sees images of bad omens, but he tells Juana he sees a rifle, a marriage in church, and an education for Coyotito. When trackers approach them, Kino attacks the men but, before he kills them, one inadvertently shoots and kills Coyotito. Kino later flings the pearl into the ocean.