Charlotte is a 19-year-old unmarried American woman from a wealthy family who is currently pregnant. Her family views her situation as an embarrassment and attempts to arrange a quiet medical procedure to eliminate the problem. Highly skilled in mathematics, she rebels against the expectations placed upon proper young ladies of her era. She focuses her energy on finding her missing cousin in post-war Europe as a way to secure a sense of purpose.

Evelyn is an abrasive, heavy-drinking survivor of World War I living in London in 1947. Her hands are severely deformed from wartime injuries, causing her to rely on hired help for daily tasks. Decades earlier, she worked as a government spy in German-occupied France under the alias Marguerite Le François. She carries immense trauma from her espionage years and harbors a deep desire for revenge against the man who tortured her.

Finn is a young Scotsman who works for Evelyn as a driver and general handyman. He owns a late-model Lagonda automobile that becomes the primary mode of transportation for the group's journey across France. A former soldier who helped liberate concentration camps during World War II, he struggles with his own wartime trauma and a volatile temper that previously resulted in a prison sentence.

René is the wealthy, middle-aged owner of a Lille restaurant called Le Lethe, which serves as a favored meeting spot for German officers during World War I. He is a French collaborator who uses his connections with the occupying forces to maintain a luxurious lifestyle. Highly observant and skilled at detecting lies, he poses a constant threat to the undercover agents working in his establishment.

Alice, who prefers to go by the code name Lili, is the tiny, bird-boned spymaster of the intelligence ring operating in occupied France. She operates under the guise of a harmless, fluttery woman to smuggle messages across enemy lines. She serves as Evelyn's primary contact, trainer, and friend during the 1915 timeline.

Violette is a squarely built former nurse who acts as the second-in-command for the intelligence network in Lille. She possesses a bossy, no-nonsense attitude and initially doubts Evelyn's capabilities as a covert agent. Following World War II, she runs an antique shop in Roubaix.

Captain Cameron is a tall, blonde intelligence officer who actively recruits women for espionage because he believes they can pass unnoticed in occupied territories. He assigns his female operatives the names of flowers, referring to them collectively as his garden. He carries the stigma of a past prison sentence related to insurance fraud.

Rose is Charlotte's French cousin who disappeared in 1943 during the Second World War. According to her family, she joined the French Resistance, became pregnant out of wedlock, and found work at a restaurant in Limoges called Le Lethe. Her unexplained disappearance serves as the catalyst for Charlotte's journey across France.

Mrs. St. Clair is Charlotte's wealthy, image-conscious mother. She is deeply embarrassed by her daughter's out-of-wedlock pregnancy and is determined to have the issue quietly resolved in Switzerland to protect the family's reputation.

Major Allenton is a military instructor responsible for training new intelligence operatives during World War I. He holds traditional views on gender roles in combat and espionage, actively excluding female recruits from firearms training until overruled by Captain Cameron.