(CNN) -- Karl Marlantes stared at the young man through the sights of an M-16 rifle and slid his muddy finger over the curve of the trigger.
Turning toward him, the man locked eyes with Marlantes and froze.
"Don't throw it. Don't throw it," Marlantes whispered, hoping the man would surrender.
Moments earlier, the North Vietnamese soldier had been hurling grenades at a group of U.S. Marines. He was cornered near the top of a hill. Blood streamed down his face from a head wound; the crumpled body of a friend lay at his feet.
Marlantes had slithered undetected to a spot just below the soldier's foxhole. When the soldier popped up, arm cocked to throw another grenade, he spotted Marlantes.
The soldier's dark eyes widened in fear; he looked around for a way out, but there was none; and then he snarled, showing his teeth.
Marlantes watched as the grenade left the soldier's hand and tumbled straight toward him.
'How can you return home?'
He had a family, a big income, and stayed in first-class hotels while jetting off to Europe and the Far East. When companies faced a crisis, they called Marlantes. He was the Ivy-League educated business consultant, the ex-Marine with the medals.
Yet few knew that Marlantes was facing his own crisis. Something was happening to him that neither he, nor his wife or five kids, could understand: There was hardly a day when he wasn't thinking about the secrets he left in Vietnam.
"How can you return home if you've never left?" he once wrote.
Marlantes is 67 now, with thick salt-and-pepper hair, a scruffy goatee and a calm, measured way of talking, but the fatigue can be seen in the lines under his eyes. He's been sorting through his war memories for over 40 years.
He first tried to purge them. He took 33 years to write "
Matterhorn," his 2010 debut novel about a Marine unit in Vietnam. He released his combat memoir, "
What It is Like to Go to War," last year.