The story is about the titular young girl who goes to stay with her grandfather, in the Swiss Alps. She becomes close friend of the young boy, Peter the goatherd and often she goes with him and his goats on the mountains. Later, she goes to stay with the rich family Sesemann in Frankfurt, to be a hired companion to Clara Sesemann, who is regarded as an invalid. However, the Sesemanns' strict housekeeper, Fräulein Rottenmeier, views the household disruptions as wanton misbehavior, and places Heidi under more and more restraint. Soon Heidi is terribly homesick, and grows alarmingly pale. Her one diversion is learning to read and write, motivated by her desire to go home and read to Peter's blind grandmother. Clara's own grandmother visits the children and becomes a friend to Heidi. After becoming very homesick and ill, Heidi returns to her beloved grandfather. Heidi and Clara continue to keep in touch and exchange letters. Clara's doctor recommends that Clara visit Heidi. He feels assured that the fresh mountain air and the wholesome companionship will do her good. While a shy Rottenmeier stays behind after a heart to heart conversation with Clara's grandmother, Clara herself makes the journey again the next season and spends a wonderful summer with Heidi and becomes stronger on goat's milk and fresh mountain air. But one day, Peter, who grows jealous of Heidi and Clara's friendship, pushes Clara's empty wheelchair down the mountain to its destruction. While attempting to bring the wheelchair back to Clara, Heidi is about to drop into a ravine, and Clara, running to save her, without realizing it, starts to walk. Her grandmother and father are amazed and overcome with joy to see Clara walking and the doctor promises to provide permanent care for Heidi, if there comes a time when her grandfather's no longer able to do so. The film eventually ends with a still of Heidi playing ball with her friends.
The soundtrack is composed by Jocelyn Pook. The mountain scenes were shot mostly in Julian Alps in Slovenia, scenes of Frankfurt in Ljubljana and willage scenes in Neath, and Llanelli, Wales. The Sessemann house in Frankfurt was shot at Stradey Castle in Llanelli.
