Out of the Dark by Gregg Hurwitz

A man melted into the throng of tourists gathered along the E Street walkway. He was neither tall nor short, muscle-bound nor skinny. Just an average guy, not too handsome. A Washington Nationals baseball cap was pulled low over his eyes to thwart the security cameras. He’d shoved rolls of dental cotton above his molars to alter his facial structure and thwart the biometrics software that the Secret Service ran on every face in the crowd. He wore fitted clothing that showed the contours of his body, no out-of-season overcoat that might conceal gear or weaponry and draw unwanted focus.