Helene is an American writer, essayist, and passionate bibliophile living in a small apartment in New York City. She supports herself through magazine work, television scriptwriting, and writing children's history books. Known for her brash, witty, and generous personality, she initiates a transatlantic correspondence and sends food parcels to help the booksellers facing postwar rationing.

Frank is the chief buyer at the Marks & Co. antiquarian bookshop in London. In his late thirties at the start of the correspondence, he is responsible for tracking down the specific, rare books Helene requests. He embodies a traditionally English style of communication—measured, courteous, and understated—which contrasts with Helene's American exuberance.

Cecily is a staff member at Marks & Co. who breaks the shop's formal protocol to reach out to Helene personally. She is warm and eager to connect, sharing personal details about the shop's staff and extending holiday invitations. Her correspondence helps widen the two-person exchange into a broader community.

Mary is Frank Doel's elderly neighbor in London. Though she is not an employee of the bookshop, she becomes part of the transatlantic community when she creates a handmade gift to thank Helene for the food parcels sent to England.

Nora is Frank's Irish second wife. She joins the correspondence a few years after it begins, acting as a family bulletin by sending photographs and updates about the household. Her letters add a warm, domestic layer to the transatlantic friendship.

Sheila is Frank Doel's eldest daughter. Her mother passed away during the war, and she is raised by Frank and his second wife, Nora. Over the course of the correspondence, she grows up and trains to become a schoolteacher.

Mary is the biological daughter of Frank and Nora Doel. She appears in the correspondence through her parents' updates, representing the passage of time as she grows from a child into an engaged young woman.

Megan is an employee at Marks & Co. who writes to express the staff's gratitude for the American food packages. She is part of the shop's bustling daily life before eventually traveling abroad to South Africa and Australia.

Bill is a staff member at Marks & Co. He is deeply moved by the kindness of a stranger sending food during the rationing period and offers to help Helene find anything she needs from London in return.

George is the eldest employee at Marks & Co. He is well-regarded by the rest of the staff, who ensure he receives a share of the much-appreciated food parcels from America.

Maxine is a close American friend of Helene. She travels to London and visits Marks & Co., providing Helene with a firsthand description of the store's Dickensian atmosphere and the ongoing realities of British rationing.

Mr. Marks is the proprietor of Marks & Co. Though he remains largely in the background of the correspondence, he occasionally steps out to greet visiting Americans who invoke Helene's name.