Very well written. The book is set in Washington, D.C. during the very early part of WW2. It has a side focus on the dynamic changes in population, both in volume and character background of the populace moving through and migrating to the city. In particular, there is an observed prelude to the racial conditions that evolved in the fifties and sixties to shape politics and culture.
The authors had a means to put the reader into a "you are there" scenario, so that you felt the tension of the events and were able to observe changes as depicted or narrated by the characters. The backbone theme of German spies attempting to assassinate Roosevelt seems like either a retelling of an actual spy ring attempt, or the retelling of a long popularized story/myth that has been told before.
The account told here tended to draw the reader forward, and the only disappointment I felt was that in the end the main characters acted like ordinary normal people faced with uncertainty and forced into different paths due to wartime career choices. This didn't occur till the climax and epilogue, which occurred in the last few pages.