The Leveling, by Dan Mayland

This is a sequel to "The Colonel's Mistake," featuring the same lead characters: Mark Sava, a former CIA agent, his more-or-less girl friend Daria Buckingham, and former Navy Seal John Decker.  The action takes place in Turkmenistan, Azerbaijan, and Iran.

One of the things I like about Mr. Mayland's writing is that he doesn't resort to completely bizarre plot twists to move his characters forward.   The bulk of the action seems realistic (although the Decker character has recuperative capabilities that push the limit).

It is not necessary to read these books in sequence, although the background on the main characters is better exposed if you do.

The Leveling (A Mark Sava Thriller)