London, 1939. On the eve of the Second World War, Canadian Maggie Wyndham defies her family and stays in England to do her bit for the war effort. Torn between two countries, two men and living a life of lies working for the Special Operations Executive, Maggie's RAF sweetheart locket is part of who she is... and who she isn't. San Francisco, 2019. Over 20 years after Maggie's death, her daughter Millie and granddaughter Willow take a DNA test that's supposed to be a bit of fun but instead yields unexpected results. Willow has always treasured her grandmother's sweetheart locket, both family heirloom and a symbol of her grandparents' love story. But now she doesn't know what to believe. She embarks on a search for the truth, one she doesn't know will reveal far more about herself.