Just as thirteen year-old Edith Walker is about to leave childhood behind, she thinks she spots a unicorn high on a slope while hiking. Her daydreamer father Henry convinces her that what she's seen is real. Edith's sighting of the fabled creature - and her unfailing belief that the imaginary creature will eventually be found - sets in motion a series of events that impact the next decade of her life. Edith grows up in her big sister Vivienne's shadow.