A world at war. One woman will risk everything. Another will uncover her story.

1940: When the island of Guernsey is invaded by the Nazis, two sisters are determined to rebel in any way they can. But when forced to take in a German soldier, they are shocked to find a familiar face on their doorstep — a childhood friend who has now become their enemy.

2016: Two generations later, Lucy returns to Guernsey after the death of a distant cousin. As she prepares the old family house for sale, Lucy discovers a box of handwritten notes, one word standing out: resistance. Lucy's search for the author will uncover the story of a forgotten sister who vanished from the island one night, never to be seen again.