The year is 1960, and Gunsmoke is the most popular show on TV. Elvis Presley tops the Billboard charts, and a charismatic young senator named John F. Kennedy is running for president. And, in North Carolina, four young Black men sit down at a Woolworth's lunch counter and demand service. Enter Esther Jane (EJ) Cloud, a 40-something spinster who manages the Dead Letter Office at the Winston-Salem post office. EJ leads a quiet life in her Old Salem ancestral home and spends her free time volunteering in the town's 18th-century medicinal garden.

One sunny Spring morning, EJ's simple life is turned upside down when the town's master gardener unceremoniously hands her a stack of handwritten letters that have all been addressed to a nonexistent person at the garden. This simple act sets in motion a chain of events that will lead EJ on a life-altering quest to uncover the identity of the mysterious letter writer―and into a surprising head-on confrontation with the harsh realities of the racial injustice that is as deeply rooted in the life of her community as the ancient herbs cultivated in the Moravian garden.

When EJ is forced to read the letters to look for clues about the anonymous sender, what she discovers are lyrical tales of a forbidden passion that threaten to unravel the simple contours of her unexamined life. EJ's official quest soon morphs into a journey of self-discovery as she becomes more deeply enmeshed in the fate of the mysterious letter writer, "Dorothea". Her surprising accomplice in solving the mystery of the letters becomes one, Harrie Hart: a savvy, street smart 10-year-old, wielding an eye patch and a limitless supply of aphorisms. Together, Harrie and EJ make seminal pilgrimages to the tiny town of Paradise to try and uncover the identity of the mercurial sender and, ultimately, learn a better way to navigate the changing world around them.