Can four girls protect a whole country? It's 1941 and the country has been turned upside down. For the aristocratic Walsingham family this means being pushed unceremoniously upstairs while their grand home is taken over by the Army. But for newcomers Ava and Maudie this is a chance to get something more from life. They are at Walsingham Hall to become code girls and break German encryptions. So being sent downstairs to work in the kitchens isn't exactly what they had in mind. But they do their duty, make new friends and soon even romance looks to be on the horizon. Though life is tough, it has never been more exciting. Meanwhile, upstairs, Lord Walsingham is hiding something. And Maudie and the girls realize that the safety of their country might actually be in their hands after all…