Alex and Sasha are twin sisters, physically identical down to their freckles. But the resemblance is only skin deep-Sasha is profoundly autistic, while Alex is not. Sasha can't communicate and acts bizarrely, and the family revolves around her and her intense needs. Yet the aged, wealthy, and mysterious Aunt Nana seems to have a particular interest in both girls. Offering a helping hand, she encourages the family to move to San Francisco to be near her. And when the young twins discover a tunnel in Nana's tool shed, it leads them on a journey across the world and back 100 years in time. The...