14-year old Susan Shawson travels back in time in her building's elevator. As altered by a retired physicist living in her building, it transports her from Philadelphia of 1998 back to the same place in 1881. There she meets Victoria Walker, a girl her own age in need of assistance with her own family problems. Gradually discovering the power of her time machine, Susan, Victoria, and her young brother Robert travel back and forth in time and succeed in changing both the past and the future.