Lionel, portrayed by Alex Descas, is a devoted widower who operates RER trains throughout metropolitan Paris. For many years, he has raised his daughter, Josephine, played by Mati Diop, in a nurturing yet isolated environment, nestled in a modest apartment building located in the suburbs. Their connection is profound, and they lead a secure and fulfilling life, primarily relying on each other for companionship and emotional support. Josephine, an anthropology student, has now matured into a young woman, maintaining a steadfast commitment to her father.
Within their apartment complex, they have formed a loose-knit community, including Gabrielle, a cab driver portrayed by Nicole Dogue, who once shared a romantic history with Lionel. Additionally, there's Noé, depicted by Grégoire Colin, a young man with a moody disposition who harbors feelings for Josephine but often finds himself caught in the chaos of his life, frequently traveling abroad. Gabrielle, while showing interest in Lionel, also extends motherly affection towards Josephine. Nonetheless, both Lionel and Josephine seem hesitant to pursue anything more than a casual friendship beyond their tightly-knit father-daughter relationship.
During a retirement party for a close friend and colleague, Lionel chooses to abstain from the tradition of consuming 35 shots of rum. Witnessing his colleague's deep sense of loss and desperation after leaving his job causes Lionel to reflect on the passing of time. He understands that he must search for purpose and stability beyond his current existence, fearing that he may one day find himself in the same predicament. Following an outing with Gabrielle and Noé, a car breakdown forces the four friends to take shelter in a closed bar. In this intimate setting, Noé's feelings for Josephine become evident, prompting Lionel to confront the reality that his daughter will eventually need to carve out her own life separate from him. This idea is subtly reinforced during a poignant visit to Noé's apartment, where it is implied that Josephine is contemplating marriage to him, especially as Noé expresses intentions to take a job opportunity in Gabon.
Tragedy strikes when Lionel's former colleague takes his own life on the RER tracks, forcing Lionel to stop the train upon discovering the body. Following this somber event, Lionel and Josephine embark on a lengthy road trip to Germany to pay their respects at her mother's grave before her impending wedding.
In the poignant final scene, Josephine marries a nervous yet joyous Noé. At the subsequent celebration, Lionel chooses to join in the revelry, successfully consuming 35 shots of rum, leaving the audience to ponder whether his actions stem from joy or sorrow. Ultimately, he returns to an empty home, facing life alone once more.
