A parallel army lives on the margins of the Iraq war-nearly 100,000 armed men, invisible yet in plain sight, doing jobs the overstretched and understaffed military can't or won't do. The U.S. media call them "security contractors." They call themselves "mercs," and they operate under their own rules. Washington Post reporter Steve Fainaru traveled with several groups of security contractors to find out what motivates them to put their lives in danger every day. What emerges is a searing, revealing, and sometimes darkly funny look at the men who live and work in the battlefields of Iraq: some are desperate, some are confused, and some are just out for a lark. Some disappear into the void that is Iraq and are never seen again. It's not a pretty picture that Fainaru reveals, but it is brutally real and shockingly honest. Big Boy Rules is an unforgettable leap into the mayhem of Iraq and into the dark recesses of the minds of American policymakers and the warriors they hire.