Andreas, Gunnar Möller is a middle-aged man who sits on a train and revisits a summer that became the core of his memory. The frame story opens with him reflecting on a youthful romance that would shape how he sees the world for years to come. The main tale begins with him as a university student traveling on a riverboat along the Danube, bound for several weeks with a host family in the small Hungarian village of Hódmezővásárhely-Kutasipuszta. On board, he meets and befriends fellow German Greta, Wera Frydtberg, who is headed for a vacation on Lake Balaton. When the boat arrives in Budapest, they share an evening together, and Andreas finds himself falling for Greta. Their romantic dinner and a stroll are interrupted by an intrusive fiddler, and the two part ways with a promise to keep in touch.
The following day, after a long train ride, Andreas arrives at his host village and is warmly welcomed by his hosts, doctor Johann von Csíky, Fritz Hinz-Fabricius, and his wife Ilonka, Adrienne Gessner, as well as many others including István, the station master Gustav Knuth. The next morning, while exploring the village and snapping photos, Andreas, who does not speak Hungarian, encounters a feisty girl who does not reply to his questions in German. He learns, to his embarrassment, that the girl is István’s daughter, Piroschka, Liselotte Pulver — the village’s best German student who understands him perfectly. Piroschka’s easy warmth and her lack of concern for his blunders draw him in, and she gladly accompanies him to a festive gathering hosted by the family. There, she persuades him to dance the lively Csárdás, and the two quickly grow closer, spending the following weeks teaching each other their languages and sharing small, meaningful moments. Andreas begins to develop real feelings for her.
Then a postcard arrives from Greta, inviting him to visit her in Siófok, which places Andreas in a conflict between a potential future with Greta and the growing bond with Piroschka. He tries to keep Greta’s message secret from Piroschka, taking the earliest train the next morning. But Piroschka has already read the postcard and quietly follows him to the hotel in Siófok, where Greta and Andreas are confronted with the girl’s presence. After a moment of confusion, Greta and Andreas tell Piroschka to take the next train back, but they agree to spend the day together until the departing train. In the evening, Piroschka again persuades Andreas to dance the Csárdás, and Greta notices how happy he looks. Piroschka ends up sleeping in Greta’s room, and during the night she slips into Andreas’s bed, tearfully apologizing for the trouble she’s caused before slipping away. The next morning, Greta tells Andreas plainly that she knows he loves Piroschka, and he rushes home, only to be told that Piroschka does not want to see him.
Back from the trip, Andreas spends the remaining days of his vacation in a somber mood. On his last night, he finds Piroschka at another celebration, but she ignores him until, with the quiet support of Johann, they are left alone and finally reconcile. However, Piroschka must soon leave to take her drunk father home, a role occupied by Sandor, Rudolf Vogel. The two are heartbroken at the thought of parting just as Andreas must depart the next morning. Yet, when his express train surfaces again in the night, Piroschka has pulled the railway signals to stop the train so she can “kidnap” him from the rails. They spend the night together, and Andreas promises to return the following year.
The frame story closes with Andreas explaining that he never did manage to return, but that the memory of Piroschka as “young and sweet” will remain with him forever, a bittersweet testament to a first, lasting love.
