"The only things that would have helped were a crash course in London during the Blitz and a little more time. I had not gotten either.
"Traveling in time is not like taking the tube, Mr Bartholomew," the esteemed Dunworthy had said, blinking at me through those antique spectacles of his. "Either you report on the twentieth or you don't go at all."
"But I'm not ready," I'd said. "Look, it too me four years to get ready to travel with St Paul. St Paul. Not St Paul's. You can't expect me to get ready for London in the Blitz in two days."
"Yes," Dunworthy had said. "We can." End of conversation."
And so a young history student from the future is travels back in time to guard St. Paul's from Hitler's bombs.
For the next few months, he labors to save the cathedral, sleep-deprived, overwhelmed by both the particular strangness-es of the past (cats! colds!) and by his own growing emotional involvement with the people and the place. As his detachment fades, both Bartholomew and the reader are drawn into the heart wrenching position of realizing that, in the end, that which you love can't be saved forever. (At which point I begin sniffing). Because Bartholomew, being from the future, knows what is going to happen to St. Paul's...
Here's an interview with Connie Willis from 2001, which covers her entire oeuvre up to that point. About "Fire Watch" she says: "My favourite story of all time that I have ever written is Fire Watch. I don't think it is my best story. I was very much a beginning writer, when I wrote that one."
I agree that, technically, it might not be her best story--it is almost clunky in places, and the relationship between Bartholomew and Enola, a young London girl he meets, is not as convincing as might be. But boy, for me at least, all the parts that don't quite work are forgiven for the sake of the emotional power of the whole.
"Fire Watch" by Connie Willis won the Hugo and Nebula awards for Best Novelette in 1983. Willis went back to her time travelling historians with Doomsday Book (1992, winner of the Hugo and Nebula Awards for Best Novel), and To Say Nothing of the Dog (1997, only won the Hugo). Doomsday Book is too unbearably sad for me to want to re-read it, but To Say Nothing of the Dog is a comic masterpiece. These are all, techincally, adult books, but good for teenagers too.