Special Agent Diana Chen's eyes hurt. They were red and dry from staring at screens all night. Cold coffee cups crowded her desk. She hadn't slept. She couldn't sleep. Not until she found what she needed in the videos from the bombed hotel.

"Play it again," she told the tech guy sitting next to her. Her voice was rough from too much coffee and not enough rest. "Slow it down when it hits 9:42."

The screen flickered as the video went backward. It showed a ...