Sandra Kienzler, a widow with a young daughter, Linn, works as a translator and interpreter in Paris. She cares for her father, Georg, a former philosophy teacher who has been diagnosed with a
neurodegenerative disease called
Benson's syndrome, which affects his cognitive abilities and sight. At a park, Sandra runs into her late husband's friend Clément, a married
chemical cosmologist who has returned to Paris after an expedition to the
South Pole. They make plans for dinner. Clément takes Sandra to his lab after she expresses interest in his profession. There, they share a kiss. They subsequently begin an affair. Sandra's mother, Françoise, who has divorced Georg and remarried, still helps care for him. She informs Sandra that his condition is worsening. He can no longer dress himself or use the bathroom and has frequent hallucinations. She says it is time to put him in a
nursing home, where he will receive the full-time care he needs—to which Sandra agrees. They encounter problems in placement, as public homes may take up to two years to vacate a room and private ones are too expensive. He is placed in a hospital in the meantime. Sandra bumps into one of Georg's former students. The student is very fond of him and asks to write to him. Sandra gives her her e-mail as a go-between. Following Georg's admission, Sandra and her family clear out his apartment, which is packed with his beloved books. She takes a few and contacts the former student, offering her the remainder. At the hospital, Georg talks constantly about his long-term girlfriend, Leïla. He is confused about where he is. Sandra notices that his condition has deteriorated. He is moved temporarily into a public home, as the hospital can no longer have him. However, because he is somewhat independent in comparison to the other residents, the facility gives the family a week to find him a new home. They ultimately place him at a private nursing home at
Montmartre, a short distance by
métro. Sandra's relationship with Clément starts to deteriorate. He cannot muster the courage to leave his wife and son, and she does not want to be just his mistress. While at the park with Sandra and Linn, Clément sees friends of his wife, and they escape the park immediately. At home, they have a discussion, and Clément declares he'll return once he leaves his wife. While tidying her home, Sandra finds a little notebook used by Georg to keep track of his declining health, along with other notebooks that she identifies as a rough manuscript of an autobiography Georg had once mentioned wanting to write. She tells her mother and sister about her findings during
Christmas dinner, and that one of the notebooks had a title written in German: "
An einem schönen Morgen" (lit. on a fine morning), which she translates to French as "One Fine Morning". Clément ends his marriage and returns to Sandra. Summer comes along. Sandra, Linn and Clément visit Georg at the private home. They talk about their trip to Italy. Georg asks for Leïla, and continues to state he does not know what he is doing there, or why he is there. He no longer recognizes his daughter or granddaughter. As they talk in his room, one of the nurses invites them to a group activity. Georg, along with Sandra, Linn, and Clément, joins the other residents who are gathered in a circle. They are given lyrics to the song "Mon amant de Saint-Jean", and sing it
a cappella together. Sandra becomes overwhelmed and starts crying. She asks Clément and Linn to leave with her. Sandra, Clément and Linn climb up the
Sacré-Cœur Basilica's
butte. As they arrive at the dome, they observe Paris. ==Cast==