Amos Decker witnesses a murder just outside FBI headquarters. A man shoots a woman execution-style on a crowded sidewalk, then turns the gun on himself. Even with Decker's extraordinary powers of observation and deduction, the killing is baffling. Decker and his team can find absolutely no connection between the shooter -- a family man with a successful consulting business -- and his victim, a schoolteacher. Nor is there a hint of any possible motive...