Swiss girl Adelheid 'Heidi' is orphaned young. Aunt Detie brings her to grandpa Alp and his wife, who live isolated in the Alps since his murder charge. Heidi soon takes to the wild country, especially accompanying young goatherd Peter. Grandpa refuses to send her to school in the city, but aunt Detie returns and forces him to give in. She's sent to a posh lady in Frankfurt, where she'll be a companion for crippled daughter Clara after school hours.

The Psammead is an 'it', an ancient, ill-tempered sand-fairy with a spider-shaped body, bat-like ears, and snail-like eyes. It is grumpy but has the power to grant one wish a day, which must be made before sunset. Five siblings—Cyril, Anthea, Robert, Jane, and infant Hilary—encounter It and experience the highs and lows of frivolous wish-making.