Set in 1971, Delphine is the only child of French farmers and enjoys working the land. Though her father wants her to marry, Delphine is secretly pursuing a relationship with a local girl. When she goes for a rendezvous with her, her girlfriend tells her that she plans to marry, dismissing the relationship between her and Delphine as "not serious": Delphine responds by running away to Paris. Walking down a street, Delphine encounters a group of women running by and pinching men's buttocks. When one of the men attacks one of the woman, Delphine helps protect her and learns that her name is Carole. The women belong to a feminist group. which they encourage Delphine to join and participate in their protests. When one of the group members learns that her best friend, a gay man, has been committed to a mental institution by his family and is being given electroshock therapy, the rest of the group refuses at first to help rescue him. Delphine convinces them otherwise, and she, Carole and some of the other women free him. The following night, Delphine kisses Carole, who is surprised and rejects her. The next day Carole tells Delphine that she is not a lesbian, but the two wind up in a passionate embrace. Carole initially believes that it is a one night stand, but quickly develops feelings for Delphine. She tells her boyfriend and the two struggle to work out their relationship even as Carole continues to see Delphine. Delphine receives a call from her mother that her father has had a stroke. Delphine visits and realizes that she must stay to help run the farm. Taking some of the lessons she learned in the feminist collective, she represents her parents' interest to other farmers. Carole visits and decides that she cannot live without her. Leaving her boyfriend, she returns to the countryside but is surprised to learn that she and Delphine must remain discreet and closeted, as Delphine's mother who does not know she is a lesbian. Carole initially enjoys country life and works the land with Delphine and her mother. However she finds the people confining, as they mock her politics and it is frustrating that she is unable to openly be with Delphine. She also begins to have doubts about Delphine's intentions after Antoine, a local boy in love with Delphine, tells her that Delphine will never leave the farm and Delphine's mother tells Carole that Antoine intends to marry Delphine. Carole begins fighting with Delphine, which results in several people learning Delphine's secret, including a local farmer who sees them kissing, and her mother who overhears them arguing. The following morning, Delphine's mother walks in on Carole and Delphine in bed. Though she acts like everything is normal to Delphine, she tells Carole to leave her home, accusing her of having perverted her daughter before attacking her. Carole tells Delphine she is leaving and Delphine decides to run away to be with Carole. Though they leave on the train together, Delphine finds herself unable to leave. She misses their connecting train to Paris and returns home. Five years later, Carole is working at a women's health clinic and in a lesbian relationship. She receives a letter from Delphine who says that she has finally left her parents' farm and has her own in Southern France. She tells Carole that she regrets not leaving with her five years earlier, but understands that it is impossible to turn back time.
On review aggregator website Rotten Tomatoes, the film holds an approval rating of 91% based on 57 reviews, and an average rating of 6.71/10. The site consensus reads, "Summertime presents a well-acted, beautifully framed period romance that offers a refreshing perspective on its era in the bargain". On Metacritic, the film has a weighted average score of 72 out of 100, based on 16 critics, indicating "generally favorable reviews". Muriel Del Don of Cineuropa writes "upbeat and majestic with tragic undertones", the film is a "real emotional odyssey in which passion seems to conquer all, even the most tenacious of prejudices". In a review for Variety, Peter Debruge called it a "luminous, golden-hued period piece" and a "beautifully realized tearjerker". Reviewing it for The Hollywood Reporter, Boyd van Hoeij said that "Though the narrative somewhat awkwardly morphs from a period drama about the French women's liberation movement in early 1970s to a more rural melodrama about being closeted and choosing between duty and family and personal happiness, the story is anchored by strong performances from Cécile de France and Izïa Higelin, who have a natural chemistry that’s not only credible but actually infectious."
