“Doomsday Book” by Connie Willis
Doomsday Book tells the story of young Kivrin, an undergraduate at Oxford, who wants to travel back in time. Such technology is typically forbidden to undergrads, and doubly so for the generous and uncharted fourteenth century. But she manages to finagle a trip and heads back to 1320 for the chance at some first-hand historical reporting. Back in 2054, things start falling apart as soon as Kivin is gone.