The Enemy, Lee Child 2007

Jack Reacher while still a Major in the MP’s special unit confronts a U.S. Army undergoing massive change as the Berlin Wall comes down.  Operating as a lone wolf (plus the inevitable female helper), Reacher solves three murders, kills a bad guy, and saves the U.S. from an Armored Corps insurrection—way to go Jack!  At the end, he’s busted to captain and heading back to Panama.