The American platoon stopped its Humvees in the road.

Ahead, a small boy of about 6, dressed in rags, staggered in circles.

Army Ranger Sean Parnell and his men were wary. It was July 2006 and they'd been in combat on the remote Afghan-Pakistan border for five months.

When the soldiers moved close enough, they saw that someone had gouged out the boy's eyes and burned the sockets black with a heated instrument. His teeth had also been knocked out.

"Jesus Christ, what is this?" said a hard-bitten sergeant.

In the nearby village, the unit's interpreter, Yusef, talked to an elder and learned what happened. The insurgents had swept through this village and punished the inhabitants for cooperating with the coalition.

They kidnapped the oldest grandson of the elder and took him to the mountains, where they gouged out his eyes and raped him for weeks.

The platoon medic did what he could for the boy and other brutalized children in this place the men came to call the "Village of the Damned." The elder thanked them and they drove on, even the toughest among them stunned by what they'd seen.

"There's not a day goes by that I don't think about it," said Lt. Parnell, 30, a Murrysville native. "All I know is that moment taught me that there is definite good and evil in this world. We don't always realize it in America, but the rest of the world can be a barbaric place."

The "Village of the Damned" is just one short chapter in Lt. Parnell's new book, "Outlaw Platoon," written with author John Bruning and set for release by William Morrow/HarperCollins on Tuesday.

Yet it captures the dichotomy of Afghanistan -- the contrast between Americans and terrorists, between good Afghans and bad, between quiet heroism and treachery.

Yusef, it turns out, is a spy. He later reveals to an Iranian cell of bomb-makers that the platoon plans to set up an observation post on a certain hilltop, allowing insurgents to seed it with mines. When the platoon arrives, villagers come out to watch. One of the mines explodes and kills Cpl. Jeremiah Cole.

But the elder whose grandson was tortured is the opposite. Gratified by American kindness, he later risks death to walk 40 miles through the mountains to warn of an impending attack.

"That's Afghanistan," said Lt. Parnell. "That incident is a microcosm of the whole country."

Becoming a Ranger

It's a world apart from Murrysville, where he grew up, and Cranberry, where he lives with his wife, Laurie, and two small children.

Lt. Parnell was attending Clarion University when he watched 9/ 11 unfold on television. Enraged, he joined the Army and found purpose, transforming from a listless college kid into a reed-tough Ranger with the 10th Mountain Division. He shipped off for Afghanistan in 2006 to take command of a 40-man platoon, nicknamed the Outlaws, with the goal of rooting out the Haqqani Network near the Pakistan border.

His book details his 16 months in combat, engaging Pakistan- based insurgents in numerous firefights in the mountains of Paktika Province. His men killed some 350 insurgents and lost just one of their own; two dozen were wounded.

The book differs from other memoirs coming out of Afghanistan in that Mr. Parnell includes an internal dialogue that reveals a sensitive leader. He's deeply affected by everything he endures, starting with his first day in Paktika when a little girl dies in his arms after a rocket blows off part of her leg.

"It was hard for me to see that," he says. "I felt like part of me was dying."

Early on, Lt. Parnell also expresses his fear of combat and questions his leadership ability.

"Sean's that kind of guy, he's very humble," said Sgt. Christopher Cowan, an Outlaw member who is now a police officer in Syracuse, N.Y. "But he was a very good leader who took care of his men."

Lt. Parnell overcomes his doubts in one harrowing moment, when his unit is pinned down by machine-gun fire and he must exit his Humvee to rally the men. …