SOLVED. Adult fiction. British prisoner on an Italian island in the second world war

[Alan]

The prisoner falls in love and when he has the chance refuses to leave the island. The ruling family imported the first motor vehicle to the island.

There is a wife of the rich chap who is attracted to a character

There is also an underwater cave in the story

[Lobstergirl, au gratin]

Is it fiction? If yes what genre? Literary, classic, adventure, romance, historical, suspense, espionage, dystopian, Sci-Fi, etc.

You read it when?
Cover?
Author's gender?

[Alan]

I found it thank you
The house at the edge of the sea

[Kris]

Glad you found your book, Alan. The House at the Edge of the Sea by Stephen Scott.