The Affair by Lee Child (2011) Delacorte Press

Reacher is re-activated and sent to a murder scene to find out what happened, who did the deed, and then to cover it up because it involves a top-secret project.  But the local sheriff, a woman, is also trying to get to the truth.  The attraction leads to a bed, but the problem needs to be solved.  There is conspiracy and those who want to keep Reacher from his mission.  Not a good place to be.