The story follows a young girl named Heidi as she embarks on a journey to uncover the mysteries of her family and her past, centered around her relationship with her mentally disabled mother.

Heidi is a twelve-year-old girl with a mentally disabled mother, but who is otherwise extremely lucky.

She and her mother are taken care of by their next-door neighbour, Bernadette; after the two appeared at her door when Heidi was a newborn.

Heidi has no information about her family, other than what her mother says through her 23-word vocabulary, including the word soof.

[4] The book was adapted into a film of the same name released in 2016, directed by Stephen Gyllenhaal, starring Talitha Bateman, Jessie Collins, Alfre Woodard, John Heard, Jacinda Barrett, Dash Mihok, and Cloris Leachman.