When Betty Palmer's sister dies under suspicious circumstances whilst landing her Tiger Moth, Betty and three other women pilots of the Air Transport Auxiliary in WWII England unite to discover who killed her and why. Estranged from her family, Penny Blake wants simply to belong. American Doris Winter, running from a personal tragedy, yearns for a new start. Naturally shy Mary Whitworth-Baines struggles to fit in. Together though, they are a force to be reckoned with as they face the mystery that confronts them. Against the backdrop of war, when ties of friendship are exceptionally strong, they strive to unravel the puzzle's complex threads, risking their lives as they seek justice for Betty's sister.