2/12/13 ** Okay...yes, I tagged it as historical fiction, even though it's really science fiction (includes time travel). However, the main action takes place in WWII Britain (mostly the London Blitz & Dunkirk).
I chose to read this because I am interested in WWII and had read little about Dunkirk. Willis does a phenomenal job building tension, causing the reader to feel the same sense of being trapped that the characters do, as they slowly realize that their time travel "drops" don't seem to be functioning and they might be trapped in 1940, unable to return to 2060 Oxford, England.
My major quibble with the world-building of the tale are the parts set in 2060. Though this is in our relatively near future, and a time travel machine has been invented, the characters don't take advantage of technology that we ALREADY have! Cell phones, internet research, eReaders - instead, they walk around to Research, Wardrobe, etc. and seem to be living in some sort of 1950s England.