Unless they've lost a passport abroad, most Americans have little appreciation for the reach and scope of the US Department of State or the perils faced by its employees. Reporter Glen Johnson had been covering politics for the Boston Globe when he received a job offer that would embed him in this world of protocols, planes, and global peacekeeping. His new boss would be Secretary of State John Kerry, set to become the most prominent diplomat on the world stage. Johnson sensed it was a meeting of man and moment. For four years, he accompanied Kerry as he became the most-traveled Secretary of...