William Le Queux 
Closed Book: Concerning the Secret of the Borgias 

In an improbable twist, an Englishman resident in Italy becomes the possessor of an old book of account from a renaissance adventurer turned priest. From the moment he purchases this book from an old monastery, he ends up beset by danger. Determined to solve the mystery of the book and the dangerous happenings around him, he travels from Italy to England in pursuit of the secret of the Borgias. (Amazon)