A forgotten woman... 1951. Esther Durrant, a young mother, is committed to an isolated mental asylum by her husband. Run by a pioneering psychiatrist, the hospital is at first Esther's prison but soon becomes her refuge. A cache of unsent love letters... 2018. When free-spirited marine scientist Rachel Parker is forced to take shelter on a far-flung island off the Cornish Coast during a research posting, she discovers a collection of hidden love letters. Captivated by their passion and tenderness, Rachel is determined to find the intended recipient. Meanwhile, in London, Eve is helping her grandmother, a renowned mountaineer, write her memoirs. When she is contacted by Rachel, it sets in motion a chain of events that threatens to reveal secrets kept buried for more than sixty years.