There are tens of thousands of them in Iraq. They work for companies with exotic and ominous-sounding names, like Crescent Security Group, Triple Canopy, and Blackwater Worldwide. They travel in convoys of multicolored pickups fortified with makeshift armor, belt-fed machine guns, frag grenades, and even shoulder-fired missiles. They protect everything from the U.S. ambassador and American generals to shipments of Frappuccino bound for Baghdad’s Green Zone. They kill Iraqis, and Iraqis kill them.

And the only law they recognize is Big Boy Rules.

From a Pulitzer Prize–winning reporter comes a harrowing journey into Iraq’s parallel war. Part MadMax , part Fight Club , it is a world filled with “private security contractors”—the U.S. government’s sanitized name for tens of thousands of modern mercenaries, or mercs, who roam Iraq with impunity, doing jobs that the overstretched and understaffed military can’t or won’t do.

They are men like Jon Coté, a sensitive former U.S. army paratrooper and University of Florida fraternity brother who realizes too late that he made a terrible mistake coming back to Iraq. And Paul Reuben, a friendly security company medic who has no formal medical training and lacks basic supplies, like tourniquets. They are part of America’s “other” army—some patriotic, some desperate, some just out for cash or adventure. And some who disappear into the void that is Iraq and are never seen again.

Washington Post reporter Steve Fainaru traveled with a group of private security contractors to find out what motivates them to put their lives in danger every day. He joined Jon Coté and the men of Crescent Security Group as they made their way through Iraq—armed to the teeth, dodging not only bombs and insurgents but also their own Iraqi colleagues. Just days after Fainaru left to go home, five men of Crescent Security Group were kidnapped in broad daylight on Iraq’s main highway. How the government and the company responded reveals the dark truths behind the largest private force in the history of American warfare. . . .

With 16 pages of photographs