By Richard Hammer. More a Mafia story than a Vatican one, the real connection is between cop Joseph Coffey and mobster Vincent Rizzo, and one chasing the other through a complex swindle involving a cardinal and a bunch of forged securities. Which may sound dry, but Hammer's book won the Edgar for Best Fact Crime in its day.
The book and story have fallen under the radar in the decades since, but this paperback is a nice reading copy; some edgewear, as shown, but an uncracked and unfaded spine, square and tight.