For as long as Heidi can remember, her mentally challenged mother has had only 22 words in her vocabulary. And that's fine with the precocious 12 year-old. She and Mama live happily, in the bubble of love and protection provided by their remarkable neighbor, the nurturing but agoraphobic Bernadette.
Then one day a new word pops out of Mama's mouth - the mysterious "soof" - and it changes everything. Heidi is propelled on a solo cross-country journey of discovery and loss, truth and identity. Secrets boil to the surface, long-hidden fears are faced, and Heidi finally learns who she is and where she and her childlike Mama came from.