I'll Be Home for Christmas by M. W. Arnold

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.