In Savannah, Georgia, nine-year-old Riddley Cross discovers a stash of old lynching postcards in her late grandfather's belongings. One of these postcards shows a young girl standing beside a hanged man. Unbeknownst to Riddley, that girl is her grandmother, now afflicted with Alzheimer's disease. As Riddley unravels the mysteries of the lynching postcards, a series of tragic events begins to unfold, forcing her to question what she has been taught about the world and her family, and what she has not.