Great story, my only complaints were that the first half of the book tends to drag on and on with details of these characters lives in 1940, which, frankly weren't that interesting, or relevant to the plot. My other problem with the book was that the whole premise of time running at different rates seemed to be rather contrived, just being created as a plot device, because there's no need for urgency otherwise if you've got time travel. The last third of the book is excellent, cleverly written, and full of action, and I still reccomend this to anyone who's a fan of time-travel or World War II. It wouldn't hurt to brush up on your knowledge of pre-war British Politics and the Manhattan Project first, however.....