The Secret Agent — Francine Mathews

WHO WAS JACK RODERICK?
They called him the Legendary American: Trained by the OSS, Jack Roderick plummeted into Bangkok one rainy morning in 1945 and never left. He was feared and respected as a foreign spy, a business kingpin, and a trader in men's souls. Then, at the height of the Vietnam War, caught in a vengeful killing web, he walked into the jungle... and vanished from the face of the earth.

FOUR DECADES LATER, CAN THE MYSTERY BE SOLVED?
Stefan! Fogg signs up for the adventure of a lifetime: solving the riddle of Jack Roderick's disappearance. To do so, she'll enter a murderous realm where only the savvy survive--and truth is the most dangerous secret of all.