Tamar

When her grandfather dies, Tamar inherits a box containing a series of clues and coded messages. Out of the past, another Tamar emerges, a man involved in the terrifying world of resistance fighters in Nazi-occupied Holland half a century before. His story is one of passionate love, jealousy, and tragedy set against the daily fear and casual horror of the Second World War -- and unraveling it is about to transform Tamar’s life forever.

From acclaimed British sensation Mal Peet comes a masterful story of adventure, love, secrets, and betrayal in time of war, both past and present.

Synopsis from Open Library.