1941. After the death of her beloved mother, nineteen-year-old Romilly Brooks impulsively accepts a job as a nanny, accompanying eight-year-old Freddie and his grandmother on a sea voyage from war-torn London to the safety of New York. From the first, Romilly is entranced by the opulent ocean liner… if only she could put the idea of German U-boats circling beneath the waves out of her mind.

September 1939. London is in blackout; war has been declared, but Dulcie Treadwell can think only of her heartbreak over American broadcaster, Glenn Reeves, who didn’t say goodbye before leaving for Berlin. Posted to Bletchley Park, Dulcie must concentrate on helping the war effort by cracking the German Enigma codes. The hours are long and the conditions tough, with little recognition from above. Until she breaks her first code. Dulcie finally settles into something she was born to do. But just as she’s proving her worth, a shocking betrayal leads to Dulcie’s brutal dismissal.

Pearl has given up on her dreams of being a journalist after being denied a promotion because of her gender. Joining the WAAF as a radio telephone operator for Bomber Command, Pearl's new job at RAF Fenthorpe serves two purposes – providing an income for her grandmother, and keeping a close eye on her younger sister, Thea, an instrument repairer at another Lincolnshire bomber station.

It's 1944, and Rosie Sinclair is full of pride to be doing her bit for the war effort as a driver at Cottisbourne Park - the secret heart of Britain's fight against Germany, where a team of brilliant and eccentric codebreakers are battling to save the country. But when she's given a new mission to drive Major-General 'Bluff' Kingsley-Flynn down to Cottisbourne, Rosie finds herself on the frontline of a new battle - to uncover a possible spy at the Park who is jeopardising their vital work, and to resist her own growing attraction to the dashing Bluff himself.... 

Paris, 1941. As we drive down the cobbled street, I take in the red banners with swastikas covering every building. Suddenly, a group of guards appears. I duck beneath the window of the car, and my heart thumps as my hand jumps to my chest. But I’m not wearing my yellow star now, I left it with my sister. Tears well in my eyes. Will I ever see her again?