Can their courage and friendship keep the nation safe?
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...
As the threat to her fellow codebreaker girls grows ever stronger, Rosie realises her country needs her more than ever. Can she save the day without losing her heart?