1941. England is at its lowest ebb. At Eden Park, where Poppy, Kate, Lily, Marjorie, and her adopted brother Billy are part of the espionage unit, the authorities have discovered there is a double agent operating in their midst.
Lily volunteers to be dropped into France, only to discover that her partner is Scott, Poppy's fiance. As further agents are wiped out by the informant at Eden Park, and Billy's life is threatened, Jack Ward, the spymaster, is forced to take measures to uncover the identity of the traitor.