A mysterious key left by her murdered sister takes Air Transport Auxiliary pilot Betty Palmer on a journey of discovery and danger. Her estranged parents force themselves back into her life, motivated purely by greed and self-preservation. Penny's life is unexpectedly turned upside down by a potentially life-changing situation that causes her wounded husband to question their marriage. No one seems safe in the turmoil of the middle years of the war, and some relationships face a breaking point whilst others become stronger. Kidnap, crashes, and dogfights—the women of the Air Transport Auxiliary Mystery Club have never faced such dangers before. To survive may not be enough. They must find the strength to rise above their most trying times yet.

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.

Air Transport Auxiliary pilot Doris Winter is accused of stealing a valuable item from a famous Hollywood movie star, now a captain in the US Army Air Corps, after a dance at the air base in England where he's stationed. Gathering her close friends together, she's determined to clear her name. Ruth's POW son suffers a life-changing injury just as her own cottage takes damage in an air raid and Penny's estranged little sister unexpectedly turns up, having run away from school. Together with the ongoing thefts of items of clothing and surprise personal revelations, these all threaten to hamper their investigation. In spite of the worsening war situation, they must band together to rise above their troubles and prove love and friendship is worth fighting for.