Meg is a 12-year-old girl living in Nazi-occupied France. She speaks fluent French, English, and German. Sharing a deep love of codes with her absent father, she practices her cryptology skills by passing secret messages. She is resourceful and dedicated to her family, often relying on her quick thinking to avoid danger.

Harper is Meg's British father and an engineer who works for the Special Operations Executive. He leaves his daughter a jar of codes to solve while he is away. Captured by the Germans, he uses his engineering background to sabotage operations from inside a factory.

Sylvie is Meg's French mother who keeps their farm running in La Perche. She works as a highly skilled radio operator for the SOE. She is fiercely protective of her daughter and balances her clandestine resistance activities with the daily struggle of providing for her household.

Captain Stewart is a British spy working for the Special Operations Executive. He arrives in France with vital information but is injured during his arrival. Recognizing Meg's sharp mind, he trusts her with a dangerous assignment.

Jakob is a young German boy traveling through France to escape the Nazi regime. He frequently relies on his quick thinking to survive the perils of the road. Despite the dangerous circumstances, he remains helpful and willing to take risks.

Albert is an older German engineer fleeing his country. He wears round glasses and carries deep regrets about his past involvement with the war effort. He is a pacifist who seeks to atone for his actions by helping others find safety.

Liesel is a German woman traveling with Albert and Jakob to escape the war. She is a former university teacher who was recruited to work as a translator. She is determined to survive and highly protective of her child who remains in Germany.

Lieutenant Becker is a high-ranking Nazi officer stationed in the area. He is sharp, observant, and dedicated to hunting down resistance members. He poses a constant threat to the local townspeople through rigorous interrogations and searches.

Grandmère lives with her family on a secluded farm in La Perche. She provides stability and comfort, stepping in to care for injured strangers and keeping the household running amid the threat of German searches.

Yvonne is a French resistance fighter operating in the forests near La Perche. She intercepts travelers to verify their identities and provides vital guidance to refugees attempting to cross dangerous borders.

Margarete is Liesel's young daughter who is enrolled in the League of German Girls. Her safety is a primary motivation for Liesel during the war.