In 1969, the story unfolds through Valentín, Judikaël Goater, an eight-year-old boy with thick black-rimmed glasses who lives with his grandmother after his parents' divorce. He dreams of becoming an astronaut and follows the ongoing space race between the U.S. and the Soviet Union. He no longer sees his mother, Véronique Royer as The Mother, who was chased out of the family home by his imperious, dictator-like father, François Rimbau as The Father, who prefers the life of an Argentine playboy.
Valentín is close to his uncle Chiche and the piano teacher Rufo, who live across the street. Both speak to him as if he were an adult, and Valentín often seems wiser than his years. His uncle takes him to mass, where a priest speaks about the death of an Argentinian doctor who was killed recently. The priest also references Che Guevara as a man “who believed in an ideal, and who believed that injustice could be overcome. Please, don't leave here before you've asked yourselves, in all sincerity: Who of you would give, not his whole life, but a year or even just one day, for an ideal, the way that Che gave all he had?” > The moment is thought-provoking for Valentín, who remarks that, “But just like my uncle said, the priest couldn't change anything. Everything stayed the same.”
Leticia, his father’s latest romantic interest, visits and spends a day with Valentín, sharing time in the park, watching a movie, and sharing a meal. Valentín confides personal things about his life and his father, and Leticia reevaluates her relationship with Valentín’s father, ultimately ending the relationship. The breakup deeply upsets his father, who blames Valentín for the turn of events.
One day Valentín realizes his grandmother is ill but refuses to see a doctor. He crafts a plan to get her to see Dr. Galaburri, and the plan succeeds enough to prompt changes in their lifestyle. To thank the doctor, Valentín buys a painting to display in his office. Tragically, his grandmother dies after a hospital visit, and Valentín goes to stay with one of his friends from school.
A thoughtful man visits Valentín and gives him a shirt his mother sent. They talk about his mother, and Valentín begins to understand why she has stayed away for so long. The film ends as Valentín arranges a blind date between Leticia and Rufo, and the three share a meal together. Valentín declares his decision to become a writer, and the story closes with Leticia and Rufo starting a new, happier life together.