Connie Willis’s To Say Nothing of the Dog (1998) time-travel novel was so disappointing that this (often hasty) reader determined to read and to say nothing of this author again. However, the main ingredients of The Doomsday Book (1992) (Oxford, time travel, Middle Ages) were interesting enough to cause this (often ridiculously optimistic) reader to give Willis another go.
I hoped that the author might have honed her skills after finishing To Say Nothing of the Dog, and have travelled back in time to improve the earlier novel. Or something. But I was (surprisingly) wrong. An amusing idea is thinly imagined and stretched. The cast of characters are all types, some of them inserted into the plot (such as it is) for heavy comedic effect. The important error which has obviously been made in setting the time travel coordinates is slowly and tediously uncovered and never properly explained to the reader (well it is time travel after all).
Thwarted telephone conversations play an important part in a 21st century which has time travel technology but no mobile phones. Bell-ringers are funny because they are eccentric (particularly when they are American). The plague was nasty. There was no cure. YA writers did this so much better in the 60s and 70s.