Part One: Perhaps an Accident
The first few pages of the first chapter of The Bridge of San Luis Rey explain the book's basic premise: this story centers on a (fictional) event that happened in Lima, Peru, at noon on Friday, July 20, 1714. A bridge woven by the Incas a century earlier collapsed at that particular moment, while five people were crossing it. The collapse was witnessed by Brother Juniper, a Franciscan monk who was on his way to cross it. Wanting to show the world God's Divine Providence, he sets out to interview everyone he can find who knew the five victims. Over the course of six years, he compiles a huge book of all of the evidence he gathers to show that the beginning and end of a person is all part of God's plan for that person. Part One foretells the burning of the book that occurs at the end of the novel, but it also says that one copy of Brother Juniper's book survives and is at the library of the University of San Marco, where it sits neglected.
Part Two: the Marquesa de Montemayor; Pepita
The second section focuses on one of the victims of the collapse: Doña María, the Marquesa de Montemayor. She was the daughter of a wealthy cloth merchant, an ugly child who eventually entered into an arranged marriage and bore a daughter, Clara, whom she loved dearly. Clara was indifferent to her mother, though, and became engaged to a Spanish man and moved across the ocean to Spain where she married. Doña María visits her daughter, but when they cannot get along, she returns to Lima. The only way that they can communicate comfortably is by letter, and Doña María pours her heart into her writing, which becomes so polished that her letters will be read in schools for hundreds of years after her death.
Doña María takes as her companion Pepita, a girl raised at the Convent of Santa María Rosa de la Rosas. When she learns that her daughter in Spain is pregnant, Doña María decides to make a pilgrimage to the shrine of Santa María de Cluxambuqua. Pepita goes along as company and to supervise the staff. When Doña María is out at the shrine, Pepita stays at the inn and writes a letter to her patron, the Abbess, complaining about her misery and loneliness. Doña María sees the letter on the table when she gets back and reads it. Later, she asks Pepita about the letter, and Pepita says she tore it up because the letter was not brave. Doña María has new insight into the ways in which her own life and love for her daughter have lacked bravery. She writes her "first letter" (actually Letter LVI) of courageous love to her daughter, but two days later, returning to Lima, she and Pepita are on the bridge when it collapses.
Part Three: Esteban
Esteban and Manuel are twins who were left at the Convent of Santa María Rosa de la Rosas as infants. The Abbess of the convent, Madre María del Pilar, developed a fondness for them as they grew up. When they became older, they decided to be scribes. They are so close that they have developed a secret language that only they understand. Their closeness becomes strained when Manuel falls in love with Camila Perichole.
Perichole flirts with Manuel and swears him to secrecy when she retains him to write letters to her lover, the Viceroy. Esteban has no idea of their relationship until she turns up at the twins' room one night in a hurry and has Manuel write to a bullfighter with whom she is having an affair. Esteban encourages his brother to follow her, but instead Manuel swears that he will never see her again.
Manuel cuts his knee on a piece of metal and it becomes infected. The surgeon instructs Esteban to put cold compresses on the injury: the compresses are so painful that Manuel curses Esteban, though he later remembers nothing of his curses. Esteban offers to send for Perichole, but Manuel refuses. Soon after, Manuel dies.
When the Abbess comes to prepare the body, she asks Esteban his name, and he says he is Manuel. Gossip about his ensuing strange behavior spreads all over town. He goes to the theater but runs away before Perichole can talk to him; the Abbess tries to talk to him, but he runs away, so she sends for Captain Alvarado.
Captain Alvarado goes to see Esteban in Cuzco and hires him to sail the world with him, far from Peru. Esteban agrees, then refuses, then acquiesces if he can get all his pay in advance to buy a present for the Abbess before he departs. That night Esteban attempts suicide, is saved by Captain Alvarado. The Captain offers to take him back to Lima to buy the present, and at the ravine, the Captain goes down to a boat that is ferrying some materials across the water. Esteban goes to the bridge and is on it when it collapses.
Part Four: Uncle Pio; Don Jaime
Uncle Pio acts as Camila Perichole's valet, and, in addition, "her singing-master, her coiffeur, her masseur, her reader, her errand-boy, her banker; rumor added: her father." The story tells of his background. He was born the bastard son of a Madrid aristocrat, has traveled widely engaged in a wide variety of dubious, though legal, businesses, most related to being a go-between or agent of the powerful, including (briefly) conducting interrogations for the Inquisition. His life "became too complicated" and he fled to Peru. He came to realize that he had just three interests in the world: independence; the constant presence of beautiful women; and work with the masterpieces of Spanish literature, particularly in the theater.
He finds work as the confidential agent of the Viceroy of Peru. One day, he discovers a twelve-year-old café singer, Micaela Villegas, and takes her under his protection. Over the course of years, as they travel from tavern to tavern throughout Latin America, she becomes beautiful and talented. Uncle Pio teaches her and goads her to greatness by expressing perpetual disappointment with her performances. She develops into The Perichole, the most honored actress in Lima.
After years of success, Perichole becomes bored with the stage. The Viceroy takes her as his mistress, and she and Uncle Pio and the Archbishop of Peru and, eventually, Captain Alvarado meet frequently at midnight for dinner at the Viceroy's mansion. Through it all, Uncle Pio is faithfully devoted, but as Camila ages and has three children by the Viceroy she focuses on becoming a lady, not an actress. She avoids Uncle Pio, and when he talks to her she tells him to not use her stage name.
When a smallpox epidemic sweeps through Lima, Camila is disfigured by it. She takes her son Jaime to the country. Uncle Pio sees her one night trying hopelessly to cover her pock-marked face with powder: ashamed, she refuses to ever see him again. He begs her to allow him to take her son and teach the boy as he taught her. They leave the next morning. Uncle Pio and Jaime are the fourth and fifth people on the bridge to Lima when it collapses.
Part Five: Perhaps an Intention
Brother Juniper works for six years on his book about the bridge collapse, trying various mathematical formulas to measure spiritual traits, with no results beyond conventionally pious generalizations. He compiles his huge book of interviews with complete faith in God's goodness and justice, but a council pronounces his work heresy, and the book and Brother Juniper are burned in the town square.
The story shifts back in time to the day of a service for those who died in the bridge collapse. The Archbishop, the Viceroy, and Captain Alvarado are at the ceremony. At the Convent of Santa María Rosa de la Rosas, the Abbess feels, having lost Pepita and the twin brothers, that her work will die with her. A year after the accident, Camila Perichole seeks out the Abbess to ask how she can go on, having lost her son and Uncle Pio. Camila gains comfort and insight from the Abbess and, it is revealed later, becomes a helper at the Convent. Later, Doña Clara arrives from Spain, also seeking out the Abbess. She is greatly moved by the work of the Abbess in caring for the deaf, the insane, and the dying. The novel ends with the Abbess's observation: "There is a land of the living and a land of the dead and the bridge is love, the only survival, the only meaning."