Following the death of her mother, nineteen-year-old Lucy Harmon is sent by her father to Italy to stay with old family friends and to have her portrait done. She is eager to renew her acquaintance with Niccolo Donati, the handsome young boy from a neighboring family with whom she shared her first kiss on a visit years earlier, and anxious to solve a riddle left in her mother's diary—the answer to which may change Lucy's life forever.