"As World War Two rages, MI5 agent Sarah Gillespie is faced with her toughest challenge yet: handling Adeline Vernier, a mysterious double agent from Paris. Adeline’s coded letters could help the Allies defeat the Germans – but, in return, she demands that her boyfriend is rescued from Nazi-occupied France. Adeline is not above threatening to double-cross MI5 to get what she wants, leaving Sarah fearful for the millions of lives at stake. Letters that could change their lives forever. As they embark on a secret operation through Lisbon, they must tread carefully to avoid the clutches of the Nazis. But will they make it out alive, together? Or is the enemy closer than they realize?"