The Scientists — Bob Doerr

The Scientists is the 5th Clint Smith novel. Clint is a hunter, a government assassin, employed by a very small, ultra secret agency. Someone has been kidnapping scientists from various countries. All are tops in their field and experts in the modernization of drones. As the world's security and intelligence services make little progress in solving the disappearances, Clint is put on alert. Three separate drone attacks occur, resulting in a number of deaths. Once the lethal drones are perfected, the kidnapped scientists' usefulness comes to an end. While Clint's mission does not include rescue, he's given the green light to go after his target. His success may prevent some of them from dying.