Picture a murky world of piranhas, fire ants, and vipers. Add jaguars and an elusive, unpredictable tribe that protects its interests with poison arrows. Factor in malaria, seesawing temperatures – baking days, icy nights – and the risk of starvation.

Enter National Geographic explorer Scott Wallace. In 2002, Wallace joined a 34-man Amazon expedition led by pro-Indian activist Sydney Possuelo: a fiery Brazilian with “a hawk-like beak, balding head, and thick auburn beard”, Wallace recounts in his new travelogue, The Unconquered.

Rekindling the spirit of old-school Dr. Livingstone-style adventure, Possuelo’s team broached “one of the largest, most species-rich, and least explored biological hot spots on earth”, the Javari. Their mission: to observe a local “lost tribe” called the Arrow People, Los Flecheiros.

“The Unconquered” by Scott Wallace (Book Trailer) from Scott Wallace.

Shadow Tribe

One of the world’s last uncontacted native peoples, the Arrow People reputedly defend their land with waves of poison-tipped arrows before melting back into the forest. Pursuing the mission, which intended to reveal how the Flecheiros were faring despite logger intrusion, required nerves of steel.

Wallace is no stranger to exotic adventure. His adventures have taken him from the Amazon’s wilderness to the Alaskan Arctic, and from post-Soviet Russian arms bazaars to raids on suspected Fedayeen hideouts in Baghdadi slums.

On Wallace’s precarious Amazon mission, he was offered the chance to bow out early and just write a profile of Possuelo.

“I appreciate your concern,” Wallace told Nat Geo editor Ollie Payne. “But I’m in on this for the entire ride.”

Hunger March

Amid mounting friction between Possuelo and some feisty underlings, Wallace continued by boat and on foot through permanent twilight in the shadow of skyscraper kapok trees. Burning 6000 calories a day, ingesting just 800, Wallace was close to starvation.

Twice lost and found, he soldiered on, sliding on his backside down muddy slopes, scrambling across slick logs strung high above foaming rivers and bathing in waters infested with caiman and piranhas. Then there were brushes with giant spiders.

Slips and Trips

Amazonia comes across as the supreme obstacle course – a maze of primal stumbling blocks. As you “grind out the yardage”, the slog is as much mental as physical. The pressure to be alert for hiccups hurdles and worse rarely relents.

“Vines yanked my hat off. Thorns ripped at my sleeves,” Wallace writes, and then conveys what effect an eye-level brush with a spiky bamboo clump could have.

The master storyteller, who makes the forest sound alive, adds that one mis-step would set him back at the foot of some hill that took 20 minutes to climb.

Finally, after three months – the entire summer of 2002, when he was flying back from Brazil’s Northwestern Tres Fronteras area, bound for his Washington DC home – Wallace finally eyeballed the Flecheiros.

“I couldn’t escape the sense of irony, even absurdity, of the moment. Three months in the wilderness, and I’d never laid an eye on the Arrow People. Forty minutes out of Tabatinga and here we were, looking down on them,” he writes.

He could, he admits, have skipped the legwork and just done an aerial recon. But that would have defeated the purpose.

Wallace, who largely survived on monkey meat, wanted to get as close as possible to the “bastion of untamed wilderness” and its invisible warriors. His epic travelogue, scribbled in notebooks while on the trail, embodies his tenacity.