Shadow of Night by Deborah Harkness is past two of the All Souls Trilogy (part one being The Discovery of Witches. While this book is clearly in the middle of a larger storyline, it clearly takes on different issues than the previous book.
This series is based around the search for a book, and the three missing pages from it. A very important, enchanted, book which contains currently unknown information about the genesis of the supernatural beings: witches, demons, and vampires.
Shadow of Night continues to follow the story of Diana Bishop, a witch just discovering her powers, and her partner/husband/ significant other, the vampire Mathew Clairmont. Unlike the previous book, this one is set in Elizabethan England. Yes, this does make sense in the book. While the last book took place in what can be thought of as Diana Bishop's home turf, this one is clearly in Mathew Clairmont's.
As a vampire, Mathew already lived through this era. In fact, some of his friends are major and minor characters. They are able to spend some time with his "father" who died during The Second World War. Diana is able to work on Alchemy (which she studies and teaches in modern times) with a famous female alchemist (who I hadn't heard of, but seems to have been quite important). Being in the different time period give Diana a chance to find someone to teacher her how to use her developing powers.
The discovery of Diana's powers. Diana has always known that she is a witch. Her family have always been witches. However, Diana stopped using her witchcraft (in which she was not proficient in the first place), as a child or teenager, shortly after her parents died. She and Mathew are now under scrutiny, and in physical danger because of their relationship. Thus, they must travel back in time (using her newly discovered genetic time-walking power) to a time when they are not being hunted. Unfortunately, some unpleasant parts of Mathew's past are now in the present, and by the end they are forced to return to the tremulous present day.
