It is 1941, and England is at its lowest ebb, under-nourished, under-informed and terrified of imminent invasion.
Even at Eden Park, the beautiful country estate where Poppy, Lily, Kate, Marjorie and her adopted brother Billy are working in espionage, confidence is at an all-time low, and that is before the authorities discover there is a double agent operating from its MI5 unit.
Lily volunteers to be dropped into France, only to find herself linked to Poppy's husband Scott.
Meanwhile, Kate's lover Eugene is in Sicily to sabotage the bombers besieging Malta while her mother is recruited to work for Jack Ward, known affectionately as 'the Colonel'.
As further agents are wiped out by the informant at Eden Park, Poppy leaves to train as a pilot.
But as she closes the wooden shutters at the House of Flowers, the old folly where she and Scott began their married life, she realises that they were made over a century before to keep out another invader.
England survived then, and will again.