Back Part 1: Across the Fence follows a covert 1968 Special Forces (SOG) mission to the Ho Chi Minh Trail in the jungles of Laos, led by Spike Miller. In alternating chapters it also follows the modern-day story as Spike, now dying of cancer, gives his grandson, Mark, a combat journal and asks him to go back to find something he left in the jungle before he was extracted at the end of that mission.

Mark, his friend Brad (an ex-US Marine) and a group of students from NYU prepare to go back into the Vietnam War-ravaged jungle of the tri-border area of Laos, Vietnam and Cambodia, on a modern-day backpacking trek to find what Spike left behind in 1968.

Picking up the company of a trio of dodgy British backpackers as they travel through Phnom Penh, Vientiane and Vang Vieng, the group ends up deep in the jungle and deep in trouble.