Assignment-Palermo (1966) by Edward S. Aarons
Edward S. Aarons wrote 41 of these "Assignment" novels. The hero is a CIA agent named Sam Durell. In addition, he wrote dozens more pulp mystery books usually under the name Edward Ronns.
I have never heard much about this author but I was definitely interested in the classic Robert McGinnis pinup covers. Some folks have said that they find Aaron's books "forgettable" but I found this book, at least, quite entertaining. His book was tightly plotted and the writing concise and efficient - really great journeyman pulp writing.
Agent Sam Durell is sent to Italy to investigate why The Brothers of the Night or the "Fratelli della Notte", an outlaw organization similiar to the Mafia, has changed it's criminal tactics in America. Somehow his greatest nemesis, Kronin, has become involved and he know that this time one of them must die...
I have a few more Assignment book to read and until then I will withhold judgement on the series. For now, if you see them in a used bookstore, pick them up.