By Connie Willis
Ballantine Books, 2010
All Clear is the sequel to Blackout. 'Sequel' is not quite the right word, as these are really just two parts to one very long book, and you absolutely should not read All Clear unless you have already read Blackout. You can read more about Blackout in that node.
These books are the latest in the longer time-travelling historians 'series', but the series is loosely knit, and other than these two book it does not need to be read in any particular order. If you are interested at starting at the beginning, the first book is Doomsday Book, a rather dark novel, followed by To Say Nothing of the Dog, a much lighter comedy. Both are well worth reading.
A Few (very) Mild Spoilers
It occurs to me that a number of people searching for this review may have read Blackout and are on the fence as to whether All Clear is worth reading. I would suspect that if you do not like All Clear, Blackout will also be a bit of a letdown. The story picks up right where we left off in Blackout, and is essentially 600 pages of exactly the same thing -- new events, of course, and new things learned, and things that we suspected are confirmed. There are new twists too, and the story continues to be engaging throughout. However, it does continue with the same characters, the same constant sense of worry, and the same frustrating situations. And yes, it is long. I will say that the ending is not unsatisfying, and things are not as dire as they seem at the end of the first book.