I'm enamored of this genre, the WWII Nazi spy thriller, but this book sorely disappointed me. First, I was put off by the British spelling and usage. Why would an American writer writing about American characters in an American setting in a book published by an American press do this? It was jarring to see "tyre" and "in hospital" in dialog spoken by regional US characters. Then I saw that the novel had originally been printed in the UK. Apparently the US editors couldn't be bothered to change this--nor did they seem to mind leaving "snuck" in the narration (not dialog). Strange.
Another thing that bothered me was the protagonist's allegedly German surname, Nessheim. This is a Norwegian surname, the name of a town and of farmsteads in Rogaland and Hordaland. The town in Norway has a namesake in North Dakota. On top of this, in the beginning of the book, the Nessheim family is said to be from Swabia. Lutherans from Swabia? Very unlikely. By the end of the book, Nessheim is saying his ancestors came from Bavaria and northern Germany...Like the British-isms, jarring and confusing.
Full disclosure: After working as an editor and composition teacher, I admit to being a bit of a crank about style and consistency. However, the real problem for me is that the story dragged along, never managing to give the reader any thrills. Nessheim's character is bland, his motives unclear. If there is an antagonist, it's J. Edgar Hoover, not the Nazi characters. I figured out who the Nazi plant was about three-quarters through the book. The ending was emotionally unsatisfying. I really don't care what happened to Nessheim or his love interest or anyone else in this rambling non-thriller.