Summer 1939. Translator Harry (Jonah Hauer-King) is working at the British Embassy in Warsaw, falling in love with Polish waitress Kasia (Zofia Wichłacz). When German tanks roll into Poland and Britain declares war on Germany, Harry and Kasia are faced with terrible choices.
　　With her life in grave danger, the only way for Kasia to be safe is to escape. Can Harry help her - and if he does, how will he ever explain himself to factory worker and singer Lois Bennett (Julia Brown), the girl he left behind in Manchester?
　　As the Nazi threat spreads across Europe, Kasia must choose between love and fighting for her country, Harry must find his place in the world, and Lois seizes new opportunities the war throws up. The conflict overturns everything for Harry's snobbish mother Robina (Lesley Manville) and for Douglas (Sean Bean), Lois' pacifist father, and her firecracker younger brother Tom (Ewan Mitchell), who joins the navy and finds himself under fire in one of the first major battles of the war.
　　In Berlin, outspoken American journalist Nancy (Helen Hunt) risks her life trying to help her neighbours the Rosslers from the attentions of the ruling Nazi regime, while in Paris Nancy's nephew, medic Webster (Brian J. Smith) refuses to leave the city and the man he loves.
　　This is a series that takes us across the first year of the war, from ordinary life in Manchester to the beaches of Dunkirk, getting right under the skin and into the hearts and minds of those living their lives during this extraordinary time as they grapple with the unthinkable: a world in flames.