I had heard about this book by Donna Cross before, but it wasn't until I was in Minneapolis with three friends, browsing through a book store, that they began raving about this story and I was intrigued, so bought the book.
It is a gripping story, and presents an intriguing question -- was there ever a woman in the Catholic church who was able to fool everyone and rise to the position of Pope?
The story is believable and held my interest, but even more fascinating was doing research on the "legend." Author Cross has done extensive research on the story, and on what she says is the attempt by the Catholic church to cover the whole thing up.
In doing my own internet research, I could see the scorn with which the church holds the theory that a woman could ever be pope. Frankly, I found Cross's research more compelling.
My strong recommendation, however, is wait to do your own research after finishing the book. I did it about 2/3 of the way into the book, to find out how it all ended, and it definitely ruined my enjoyment of the ending of the book.
Highly recommended book.