Tom, I recently read an Elizabeth George mystery novel that takes place on Guernsey. It's titled a Place of Hiding, and I read it because it because 1) I enjoy most Elizabeth George mysteries, and 2) because it took place on Guernsey.
My own novel is set in Guernsey, Herm and Alderney and covers around 30 years starting in the occupation. It's called Rachel's Shoe but you might struggle to get it on Amazon as they keep listing it as out of print, which it isn't.
I'm a local author and my grandparents lived through the occupation here.
If you would like to see what it's about the website is RachelsShoe.com and you can buy (signed if you wish) from there if you like the look of it.
Arabella's Notebooks, a historical novel set in Victorian London and Guernsey, is available on Kindle ebooks. Written by a Guernsey resident, it gives an insider's view of the island as part of the story line. There is a website for the book it is www.melissa-mourton.com that gives more information and has photos of Guernsey. You can 'sample' the ebook to see if it is your kind of read.
I lived in Guernsey for many years and loved it so much I wrote a book set there -Dangerous Waters - Mystery, loss and love on the island of Guernsey. It's a contemporary romantic mystery with overtones of the Occupation. Please feel free to check it out! Like another reader I thoroughly enjoyed Elizabeth George's book based on Guernsey.