Time travel stories are tricky. The author must either ignore the inevitable paradoxes or must find some plausible device for resolving them. (In a few cases, there’s a third option: the author decides to wallow in paradoxes, which can put a strain on suspension of disbelief except in the case of humorous stories like some of Robert Heinlein’s.) Connie Willis takes the most common way out by simply declaring that altering the future is impossible because of a law of physics, although some doubts about this “law” add considerable richness to her works.
Blackout and All Clear are actually two parts of a single novel. Releasing them as two separate titles was an understandable marketing decision by the publisher, since the resulting 1168 pages would be too much for even the most dedicated consumer. (Some of my students would say TLDR for even a quarter of that total.) The resulting novel is an inextricable combination of science fiction and historical fiction, but much more the latter. As the titles may suggest to you, the topic is the bombings of London by the Germans in the Second World War. More expansively, we have this description in the author’s own words:
They’re about Dunkirk and ration books and D-Day and V-1 rockets, about tube shelters and Bletchley Park and gas masks and stirrup pumps and Christmas pantomimes and cows and crossword puzzles and the deception campaign. And mostly the book’s about all the people who “did their bit” to save the world from Hitler — Shakespearean actors and ambulance drivers and vicars and landladies and nurses and WRENs and RAF pilots and Winston Churchill and General Patton and Agatha Christie — heroes all.
Indeed the books are about all that — hence the large number of pages. There are dozens of characters, some of whom are a bit difficult to keep track of, since each of the protagonists has at least two names, the “real name” in the present (actually 2060) and the “historical name” in the Blitz (in 1940). Think of it as a historical novel, written from the perspective of people from 120 years in the future. The “Keep Calm and Carry On” poster has become newly popular in recent months in its original incarnation and in many parodies; it’s a perfect representation of how the Brits dealt with the Blitz, at least in Willis’s eyes. If you don’t mind the length (which is necessary, by the way) and if you enjoy both history and science fiction, you should definitely read this totally absorbing and often amusing two-part novel.