Two years have passed since Heidi and Klara Sesemann parted, and the quiet rhythm of their Alpine world has shifted in subtle, telling ways. Klara has suffered a relapse and, at times, must still rely on the chair she once used, a setback that weighs on both girls and colors their renewed proximity.
Heidi is thriving at school, but Peter prefers to spend his days sledging. The elderly Alpöhi Alpöhi hatches a plan to nudge the boy toward steadier effort. On December 6, dressed as Nikolaus, he startles Peter so effectively that the boy vows to improve. Reading is still a challenge for him, but Heidi lends patient help, and through steady encouragement he gradually reads with growing fluency, a small victory that shifts the tone of their village life.
Klara Sesemann is finally able to travel to Switzerland, but Peter misplaces the letter announcing her arrival and Heidi learns of it only at the last moment. Now Heidi must host her guest, even though Klara's walking is uneven and she cannot join Peter on the mountain as before. Peter grows annoyed because he had built a shelter designed for Heidi’s visits, a space that now feels suddenly out of reach. In the Alps, Peter encounters surveyors who study the mountains, and he becomes drawn to this field. He imagines a future as a surveyor that would keep him close to the peaks he loves, but the training is expensive, something his family cannot easily provide. The training costs a lot of money, which Peters Mutter does not have.
Peter grows more taciturn with Heidi and Klara. When he sees the parked-up wheelchair, he pushes it down the mountain, where it shatters, hoping Klara, who depends on the chair, will leave. He begins to have nightmares about his own action, and Alpöhi soon realises who pushed the wheelchair but stays silent because the absence of the chair encourages Klara to try and walk again.
During a stormy night, Klara is frightened. Alpöhi must go to the village because it is threatened by floods, and Klara follows him before Heidi can prevent it. Heidi and her grandfather find Klara near the bridge. The village is flooded, but fortunately there are no casualties, though there is considerable material damage. Klara, changed by the shock of her adventure, helps with the cleaning. When her father arrives, he is astonished to see his daughter in such good spirits and health.
To prevent flooding from happening again in the future, it is decided that the stream will be diverted. To raise the necessary funds, a public festival is held. Heidi and Peter, accompanied by Klara on the piano, sing in the nearby Spa town to raise funds. Before he and Klara leave, Mr. Sesemann tells Peter he will fund his studies to become a surveyor.
