A Discovery of Witches (All Souls Trilogy) by Deborah Harkness

I loved this book.  I enjoyed reading it so much I made myself slow down and stop every so often so I could enjoy the story longer.  I've never done that while reading a book before. 
I actually finished this book in July, but just getting around to posting it since I've been on hiatus.

It all begins with a lost manuscript, a reluctant witch, and 1,500-year-old vampire. Dr. Diana Bishop has a really good reason for refusing to do magic: she is a direct descendant of the first woman executed in the Salem Witch Trials, and her parents cautioned her be discreet about her talents before they were murdered, presumably for having "too much power." So it is purely by accident that Diana unlocks an enchanted long-lost manuscript (a book that all manner of supernatural creatures believe to hold the story of all origins and the secret of immortality) at the Bodleian Library at Oxford, and finds herself in a race to prevent an interspecies war. A sparkling debut written by a historian and self-proclaimed oenophile, A Discovery of Witches is heady mix of history and magic, mythology, and love (cue the aforementioned vampire!), making for a luxurious, intoxicating, one-sitting read.