Back Part 1: Across the Fence by Peter Alan Lloyd

A covert '68 Special Forces mission to the Ho Chi Minh Trail in Laos, led by Spike Miller, who gives his grandson, Mark, a combat journal and asks him to recover something he left behind in the jungle. Mark, his friend Brad (an ex-US Marine) and a group of NYU students prepare to backpack into the tri-border jungle of Laos, Vietnam and Cambodia to find what Spike left behind.