March 1912: Twenty-four-year-old Elspeth Dunn, a published poet and a fisherman’s wife, has never seen the world beyond her home on Scotland’s bucolic Isle of Skye. So she is astonished when a fan letter arrives from an American college student, David Graham. As the two strike up a correspondence - sharing their favourite books, wildest hopes, and deepest secrets - their exchanges blossom into friendship, and eventually into love. But as World War I moves across Europe and David volunteers as an ambulance driver on the Western front, Elspeth can only wait for him on Skye, hoping he comes back alive.

June 1940: More than twenty years later, at the start of World War II, Elspeth’s daughter, Margaret, has fallen for her best friend, a pilot in the Royal Air Force. Her mother warns her against finding love in wartime, an admonition Margaret doesn’t understand. And after a nearby bomb rocks Elspeth’s house, and letters that were hidden in a wall come raining down, Elspeth disappears. Only a single letter, sent decades before by a stranger named David Graham, remains as a clue to Elspeth’s whereabouts. As Margaret sets out to discover who David is and where her mother has gone, she must also face the truth of what happened to her family long ago....