Dick and Nicole Diver are a glamorous couple who take a villa in the South of France and surround themselves with a circle of friends, mainly Americans. Also staying at the resort are Rosemary Hoyt, a young actress, and her mother. Rosemary gets sucked into the circle of the Divers; she falls in love with Dick and is also adopted as a close friend by Nicole. Dick first toys with the idea of an affair with Rosemary at this point, which he finally acts upon years later.
However, Rosemary senses something is wrong with the couple, which is brought to light when one of the guests at a party reports having seen something strange in the bathroom. Tommy Barban, another guest, comes loyally to the defense of the Divers. The action involves various other friends, including the Norths, where a frequent occurrence is the drunken behavior of Abe North. The story becomes complicated when Jules Peterson, a black man, is murdered and ends up in Rosemary's bed, in a situation which could destroy Rosemary's career. Dick moves the blood-soaked body to cover up any implied relationship between Rosemary and Peterson.
Once into the book, the history of the Divers emerges. Dick Diver was a doctor and psychoanalyst and had taken on a complicated case of neuroses. This was Nicole, whose complicated, incestuous relationship with her father is suggested as the cause of breakdown. As she becomes infatuated with Dick, Dick is almost driven to marry her as part of the cure. Strong objections are raised: Nicole is an heiress and her sister thinks Dick is marrying her for her money. They do marry, and Nicole’s money pays for Dick's partnership in a Swiss clinic and for their extravagant lifestyle. However, Dick gradually develops a drinking problem. He gets into fights and trouble with the police in various incidents and is bought out of the clinic by his partner.
The opening episode almost marks the crossover point whereby Dick becomes the weaker partner, progressively failing in what he attempts while Nicole becomes stronger. Dick's behaviour becomes embarrassing as he mishandles situations with the children and friends. Eventually Nicole has an affair with Tommy Barban, and divorces Dick to marry Barban. Nicole survives, while Dick drifts into ever diminishing circumstances. The underlying theme is then how one person has become strong by destroying another—a point emphasized cynically by Nicole's sister, who having seen Dick originally as the parasite, finally remarks that "That was what he was educated for."
Summery found on Wikipedia