The Athens Solution (Scot Harvath #15.5) by Brad Thor

A deadly betrayal is at the center of The Athens Solution. When a game-changing weapon falls into the wrong hands, the US Ambassador to Greece must risk everything to recover it, even if it means participating in a ruse that costs his life. With the ambassador dead and the device still at large, covert counterterrorism operative Scot Harvath rushes to eliminate a terror cell about to sell the dangerous technology to Iran. As the sun sets on the Aegean Sea, Harvath must go head-to-head with a traitorous adversary in a confrontation that puts the fate of America and her allies at risk.