I finally came to the top of the library reserve list for "All Clear", the concluding half of Connie Willis' "Blackout", which my f2f sci-fi book group read in February. The books shouldn't have been split; Blackout ends in the middle of the action, not even really at a stopping point. It was a publisher's decision. The two together are over 1200 pages.
The time-traveling historians are traveling back to WWII, but they are having trouble, because the drops aren't operating properly, and they don't seem to be able to get back. Several of them are stuck in London during the Blitz, and we get a good picture of life then. Complaints: there are far too many scenes in which people are rushing around trying to find each other, too many times when the characters are hiding some bit of information from someone because it will upset them, even though the person involved needs to know whatever it is, and the suspense-building trick of cutting back and forth from one set of events to another is overused to the point of confusion, especially since we are not only moving in space, but also seeing the same characters at different points of time.
It's still a good read, though. WWII conditions are memorably described, we care about the characters, present and past, and the explanation for the problem with the drops is convincing and important.
So I recommend the two books, but you will have to work at them a bit.
