Set in summertime on the Côte d'Azur, it is a drama of sexual jealousy and possessiveness. Both French and English-language versions of the film were made, with the actors filmed speaking English for the international release, which was unusual at a time when movies were always either dubbed or subtitled. That 114-minute international release, shorter than the French version, also had a slightly different editing.
Jean-Paul, a writer and Marianne, his girlfriend of just over two years, are holidaying at a friend's villa. There is a tension in their relationship which excites Marianne: the film begins with a scene in which they are together beside the villa's swimming pool and she urges him to claw her back. He does as she asks, but then throws her into the pool and jumps in after her. In a later scene he takes a branch and uses it to lash her bare buttocks, playfully but with a force that increases as the scene cuts away.
Harry, an old friend and record producer who was Marianne's lover before Jean-Paul, arrives for a visit, surprising the couple by bringing along his 18-year-old daughter Penelope, whose existence they had not previously known about.
The four stay together and Harry draws Marianne back towards him as the days go by. Taunting Jean-Paul for having given up serious writing to work in advertising, Harry drinks a great deal and throws a surprise party while Jean-Paul, a recovering alcoholic, stays sober. Meanwhile it becomes clear that Penelope neither likes nor respects her father, whom she has barely known while growing up. She and Jean-Paul become close and spend a day alone together by the sea. What happens there is left unshown, but if their relationship has not yet become sexual, it clearly will soon.
That night, while the women are asleep, the two men finally confront each other. Harry falls into the pool and is too drunk to swim. Jean-Paul, who has also been drinking, at first stops him from climbing out of the water, then deliberately pushes Harry under and holds him down until he drowns. He covers up the crime by hiding Harry's wet clothes, making it look like an accident.
After the funeral, a policeman, Inspector Lévêque, visits the house more than once. He confides to Marianne his reasons for doubting the story of an accident. When she tells Jean-Paul, he confesses everything to her, and she goes to see the evidence that would have given him away. But when she does not give it to the police, the inquiry is dropped.
Marianne takes Penelope to the airport and sees her off as she returns to her mother. She and Jean-Paul are then about to leave the villa when she tells him that they will not go together. She calls for a taxi but he places his hand on the telephone, cutting off her call and silencing her. In the end, neither leaves that day, and in the film's final shot they stand side by side looking out the window at the swimming pool, and then embrace.Romy Schneider as MarianneAlain Delon as Jean-PaulMaurice Ronet as Harry LannierJane Birkin as Penelope LannierPaul Crauchet as Inspector Lévêque
Delon and Schneider had been partners from 1958 to 1963, and it was he who presented her posthumous Honorary César in 2008. Delon ended their romance by sending her a note "Je regrette".
It was during the making of this film that the dead body of Delon's former bodyguard, Stephan Markovic, was discovered on 22 September 1968, resulting in the Markovic Affair.
It was the fourth most popular movie at the French box office in 1969.
The movie was released in the UK as The Sinners to limited box office response. It was released in Italy with twenty minutes cut out, but was a popular success.
The Los Angeles Times called it a "handsome, stunningly designed film" which was at its best in "the deft way in which it coolly depicts how beautiful, chic people, dedicated to a sophisticate, amoral view of love, can be utterly defenseless against an onslaught of passion – a favorite Gallic theme."
The 2016 film A Bigger Splash, directed by Luca Guadagnino and starring Ralph Fiennes, Tilda Swinton, Matthias Schoenaerts, and Dakota Johnson, is based on La Piscine.
Excerpt of the film was used in the Christian Dior Eau Sauvage cologne advertising campaign drawing on the legacy of Alain Delon.
Alain Delon said in an interview that he cannot watch this film again. His ex-lover Romy Schneider and good friend Maurice Ronet both died prematurely and under tragic circumstances. Revisiting the scenes are simply too painful for him.