Rosemary Hoyt, a beautiful 18-year-old American actress, arrives with her mother at Gausse's hotel on the French Riviera for a vacation. She meets Dick Diver, a charming and handsome psychiatrist, and his beautiful wife, Nicole Diver. Rosemary instantly falls in love with Dick and enters the world of the Divers, which is full of people and parties and gaiety. She meets other people on the Riviera (both at the beach and through the Divers), such as the McKiscos, Abe North, and Tommy Barban. Rosemary boldly confesses her feelings for Dick, and he begins to reciprocate them. Rosemary accompanies the Divers to Paris where, after Abe North is involved in the murder of a black man, Rosemary sees Nicole having a nervous breakdown in the hotel bathroom.
The narrative flashes back to Dick's days as a young student. He attended Yale, went to Oxford as a Rhodes Scholar, and got his medical degree from Johns Hopkins. He was considered to have great promise, and he sought both to practice as a psychiatrist and to publish medical treatises. At a psychiatric clinic on the Zurichsee, Dick meets the 16-year-old Nicole Warren, a Chicago heiress who is there because she suffers from schizophrenia (caused by her father's molestation of her). Nicole writes Dick letters while he is enlisted as a soldier, and the letters reveal both her love for him and improvement in her disorder. When Dick returns, they fall in love, marry, travel together, buy a house on the French Riviera, and have two children.
With Nicole's money, Dick invests in a clinic in Switzerland with a friend. At this point, Dick's life begins to deteriorate. He is accused of seducing the 15-year-old daughter of one of his patients. Nicole, motivated by insane jealousy, runs their car off a road. In order to get away from the turmoil, Dick leaves for Berlin but, learning that his father has passed away, heads to America. Dick stops in Rome on his way back, where he sees Rosemary, and they finally consummate their love. He becomes very jealous of a male actor, causing a scene with her and, subsequently, going out and drinking too much. He becomes belligerent with an Italian taxi driver and is thrown in jail. Baby Warren (Nicole's sister) rescues him. When Dick returns to the clinic, he learns that his excessive drinking has compromised his career. His business partner asks him to leave the business.
When the Divers return to America, Dick continues to weaken and unravel. He drinks heavily, makes a fool of himself, and insults his old friends. Nicole, who has become increasingly strong and frustrated with Dick's behavior, has an affair with Tommy Barban. She and Dick divorce so that she can remarry Tommy, and Dick moves back to America to live a somewhat unsuccessful and anonymous existence in small-town New York.