On Target by Mark Greaney

From #1 New York Times bestselling author Mark Greaney comes the second entry in the explosive thriller series featuring the lethal assassin known as the Gray Man.
When an old comrade Court Gentry thought was dead returns to haunt him, his own life is put in the crosshairs.
The man wants Court to complete a mission, with one crucial catch to his orders: Instead of a difficult assassination, the job will entail a nearly impossible kidnapping-and Court must return his quarry to the very CIA team that turned on him.