The Hidden by Mary Chamberlain

Dora Simon is comfortable in her retirement, indulging her interests in gardening and music. Joe O 'Cleary is content on the Jersey farm he helped rebuild with its owner, Geoffrey Laurent, with time to pursue his life-long hobby of birdwatching. But their worlds are shattered by the arrival of Barbara Hummel, a young German anxious to track down the identity of a mysterious woman whose photograph she found among her mother 's possessions.
Forced to resurrect long-buried secrets, and confront a past they never thought they would revisit, Dora and Joe 's lives unravel and entwine - in shocking and surprising ways. Trapped in the Channel Islands under the German occupation in the Second World War, Dora, a Jewish refugee, conceals her identity; Joe, a Catholic priest, conceals a secret. The consequences of the lies both are forced to live are as unexpected as they are devastating.
This is a heart rending and provocative story of love and betrayal, shame and survival, casting light into the forgotten or unknown shadows of war.