"Blackout" and "All Clear" by Connie Willis
I actually read "Blackout" during the summer and finished "All Clear" last week, but the break didn't really matter (it was easy to pick up on all characters and what their current situation were).
The great part of the books: The setting. Willis description of life in WW2 London (during the Blitz and later the V-1 and V-2 attacks) is extremely detailed and believable. Honestly, there were parts where I was wishing she hadn't written a time travel story and just focused on characters living during that time.
The not-so-good-part: time travel.