Mecca for Murder — Stephen Marlowe

A PI heads from DC to Saudi Arabia to save the life of a client targeted by a hit man.
 
Nothing will stop the beautiful Fawzia Totah and her lover, US Army colonel Lyman Tyler, from boarding a plane for the Middle East to make their pilgrimage to Mecca. So Fawzia hires Washington PI Chester Drum to serve as bodyguard until she's safely out of the country.
 
But Lyman's wealthy mother, Davisa, doesn't want Fawzia to go anywhere safely. The violently bigoted, socially connected woman comes from old Virginia money, and she's not about to let this former dancer from Jordan risk her precious Southern reputation. Not only is her son prepared to convert to Islam for the woman he loves, he's also already married. When Davisa hires a hit man to track down Fawzia and take her out, Drum has no choice but to follow. However, Davisa's motives aren't as simple as they first seem -- and the road to Mecca has a sudden turn no one will see coming.
 
This is a twisting, fast-paced mystery in the vintage series that “combined elements of the hard-boiled detective story and the international espionage thriller” by a recipient of the Private Eye Writers of America's lifetime achievement award (The New York Times).
 
Mecca for Murder is the 2nd book in the Chester Drum Mysteries, but you may enjoy reading the series in any order.