Time travel makes my head hurt in the most wonderful way.
This isn't a direct sequel to Doomsday Book, it merely takes place in the same universe and shares a couple of minor characters. The tones of the two books are actually quite different, and this installment is much more lighthearted and humorous. It's a bit of an homage to Jerome K. Jerome's Three Men in a Boat's Jeeves series and the classic mystery novels of Agatha Christie and Arthur Conan Doyle. It helps to have at least a passing knowledge of these works, but it really isn't necessary to the enjoyment of the story.
I'm still not completely sure what the bishop's bird stump is, but at least I learned all about penwipers.