Britain is at war. On the first day of September 1939, Hitler's armies invade Poland. Hannah and Richard Baker are evacuated to the coast, where they soon become friends with the Pavitt children, Beth and the mischievous Tom. John Baker is sent to France as part of the British Expeditionary Force, to face the mighty onslaught of the German 'Blitzkrieg'. Within a year, Britain faces the most serious invasion threat for several centuries. The Pavitt's cousin, Peter Stone, and a relatively few other airmen have to defend their country against the seemingly invincible Nazi enemy. The two families experience the hardships, new friendships and horrors of combat that war brings, and the morale of a nation is tested.