Half of a novel, Connie Willis’s Blackout ends at an arbitrary midpoint so its sequel, All Clear can begin.

It’s 2060. Time travel works. Every day, young historians set out from an overworked Oxford lab to witness times past. Some study the Crusades, some study Rome, but our protagonists are observing the home front in Britain in the early years of the Second World War. One plans to interview Dunkirk refugees, another will mind children evacuated from London to the countryside, a third plans to spend a few weeks as a London shopgirl during the blitz. The war at home is told well, though this is familiar territory and Sarah Waters’ Night Watch is tighter and more focused.

These time-travelling historians are strangely ill-prepared and incurious. They know a lot about their specific assignment – implants and memorization tell them exactly when the air raid sirens will go off and where the bombs will hit each day – but their grasp of the course of the war outside their assignment is often vague. None seems to have much passion for history or much interest in the twentieth century. Neither the characters nor the author show sufficient anxiety for the many small things that everyone knew in the past but no historian would be likely to anticipate. One historian is going to serve as a housemaid to Lady Caroline: does she know how to do all the things a housemaid would? What kind of soap do you use when washing the windows? At what hour (and on which day of the week) do servants bathe? How do you trim a wick or shine a shoe?

Our heroes seem chiefly interesting in confirming facts and impressions from their textbooks. This seems wasteful: even if the Temporal Continuum keeps you from changing important things, and that means you can’t actually get close to Great Events that change everything, there are tons of details about how people lived that we simply don’t know about, things that everyone knew then but no one knows anymore. In ancient Rome, where did the slaves sleep? We have no idea at all. Every Roman child, free or slave, knew the answer. But in all our surviving stories and histories and letters, no one happens to mention where you’d find your secretary or cook in the middle of the night.

Even for quite recent times, there are lots of things we don’t know because they require comparisons that contemporaries – even surviving contemporaries – couldn’t make but that any graduate student could easily handle. Go back to London or New York or Chicago in 1910 for a few days, and you could find out all sorts of stuff we don’t know:

• What was tenement life really like? We have the good memories and the bad memories and the details and the statistics. There’s much more to know. Lots of things – the smell of Old Paris, or (for that matter) all those kids necking in Parisian parks – they’re gone now. What else are we going to be forgetting?
• How good were baseball players in 1910? We can reconstruct a lot, yes, but wouldn’t it be nice to have one afternoon’s report on Cy Young and Walter Johnson from a contemporary scout?

Or, go over to London in 1880. We could find out things like:

• How did Escoffier’s sauces actually taste? How much sauce did he use? What were pre-phylloxera claret and sauternes really like?
• How golden was the golden age of cricket?
• What was the composition of London fog?
• What was it about Sarah Bernhardt?

This is an engaging book but not an economical one. The time-travel subplot spawns complications that the characters are surprisingly slow to grasp, and it seems none of them have read the classic time traveller stories. Provisions are in place for retrieval teams to rescue students who fail to appear for their extraction rendezvous, but nobody in 2060 seems to have anticipated that fallbacks or contingency plans might perhaps prove useful.