For as long as Heidi (Talitha Bateman) can remember, her 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 (Alfre Woodard). 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.