[4][5] These two volumes are the most recent of four books and a short story that Willis has written involving time travel from Oxford during the mid-21st century,[6] all of which won multiple awards.

Willis imagines a near future (first introduced in her 1982 story "Fire Watch" and featured in two of her previous novels: Doomsday Book and To Say Nothing of the Dog) in which historians conduct field work by traveling into the past as observers.

Historians in Willis' world believe that the laws of physics resist possible alterations to the past by preventing time-travel to certain places or times.

Michael Davies, who had prepared for a first-hand look at the events of Pearl Harbor, for example by having brain implants to give him an American accent and knowledge of that time, abruptly finds himself instead being sent to witness the response to the Battle of Dunkirk.

Dunworthy himself is nowhere to be found, having set off for a meeting with another academic, Ishiwaka, who theorizes that continued time travel has pushed the laws that safely govern it to the breaking point.

Merope takes on the persona of an Irish girl, Eileen O'Reilly, to secure a position in the staff of an English country manor house.

Merope, referred to mostly in both books as Eileen, excels at her assignment, even when she comes to dislike it and to try desperately to escape to her "drop," which is located in the woods outside the manor grounds.

She is appalled by what she considers the barbaric medical treatments of 1940 (she errs by referring to "a virus," a term not generally known then), and manages to save Binnie's life only by stealing some aspirin to bring the girl's fever down.

To her dismay, the local vicar, Mr. Goode, has arranged for Binnie and Alf to be given "safe passage" to Canada, so that they will not have to remain with their neglectful mother in Whitechapel, which, as Eileen knows, was bombed during the Blitz.

Her intention (that is, her research assignment) was "to observe shelterers in the tube stations",[9] but she ends up joining a group huddling under St. George's Church.

To his horror, he is brought against his will onto the small, barely seaworthy craft Lady Jane of Commander Harold and taken across the English Channel to help evacuate the soldiers from the beach at Dunkirk.

When they arrive at the mole there, soldiers begin scrambling onto the boat, but Michael must dive underwater to free the propeller from a corpse which has become entangled with it.

He awakes in Orpington War Emergency Hospital, where he is adored as a hero, but, for months, he is terrified that he has changed the course of history by saving soldiers.

Now together, the three believe that their own actions, particularly in Mike's case, may have changed the future so that there is no time travel, and that possibly it will involve Germany winning the war.

Knowing something has gone wrong which prevents them from returning to 2060 Oxford, the three time travelers attempt to determine an escape plan, but none of their efforts are successful.

(Bartholomew's time travel experience is the subject of Willis's short story "Fire Watch," written almost thirty years previously.)

Eileen refuses to accept his death, but upon realizing Alf and Binnie's mother has been dead for months, she volunteers to raise the orphans, thus giving her life, now trapped in the mid-20th century, a significant meaning.

The continuum around World War II is in such disarray that it has sealed itself off to time travel, and will engage in 'corrections' – likely the death of the historians and those they have influenced, Dunworthy believes.

She finally realizes what is going on as she lies recovering in the hospital; the historians have caused small things to happen which ultimately led to winning the war.

[5] In August, 2006, at the 64th World Science Fiction Convention, in a give-and-take with her audience, Willis described her novel-in-progress: "It's about World War II, and I have four historians... One of them is with the evacuating children in the North of England; one of them is doing the Blitz; one of them is doing the civilian evacuation from Dunkirk, of soldiers but by civilians; and one of them is doing the Intelligence War involved in the lead-up to D-Day, where they fooled Hitler into thinking we were attacking at Calais, instead of at Normandy.

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.

Michael Dirda of The Washington Post praised the diptych as "as vivid an evocation of England during World War II as anyone has ever written" and wrote that "Blackout is, by turns, witty, suspenseful, harrowing and occasionally comic to the point of slapstick.

[15] A. M. Dellamonica described the story as "an intricate puzzle" and "a celebration, too, of courage and heroism, of perseverance, of ordinary people doing small things to aid in great causes, of devotion, friendship, keeping one's word.

"[16] Julie Phillips of The Village Voice wrote, "Blackout/All Clear is neither tragedy nor comedy, but a mystery story with touches of grief and slapstick... None of the three historians manages to stand by and observe...

Unfortunately, the bulk of Blackout is taken up by Polly, Mike and Eileen's individual realizations that they're trapped in the past, with each caught in a state of seemingly perpetual denial about their circumstances.

Instead of acknowledging the blatant truth of their predicament, they concoct endless mental scenarios as to why their gates won't open... Willis goes on for pages with her protagonists repeatedly ruminating about the same "what ifs" over and over (and over) again.

It's a shame that these negatives so overwhelm Blackout and All Clear, because despite them the books feature many terrific characters moving in extremely interesting historical situations.

"[18] Similarly, Adam Roberts of The Guardian wrote, "The result is a mildly interesting 200-page novel about the ordinary heroism of British civilians during the war, bloated to 800 pages via an egregiously handled time-travel conceit, eked out with great jellied quantities of historical research, endless meandering conversations, long passages disposed into that tiresome typographical convention by which characters' inmost thoughts are spelled out in italics, and a string of inconsequential chapter-end cliffhangers/immediate resolutions that got increasingly on my nerves as the book went on.