Leading them was the charismatic commander Isaac Strain, an adventuring 33-year-old U.S. Navy lieutenant. The party could have turned back except, said Strain, they were to a man "revolted at the idea" of failing at a task they seemed destined to accomplish. Yet Strain's party would wander lost in the jungle for another sixty nightmarish days, following a tortuously contorted and uncharted tropical river. Their guns rusted in the damp heat, expected settlements never materialized, and the lush terrain provided little to no sustenance. As the unending march dragged on, the party was beset by flesh-embedding parasites and a range of infectious tropical diseases they had no antidote for (or understanding of). In the desperate final days, in the throes of starvation, the survivors flirted with cannibalism and the sickest men had to be left behind so, as the journal keeper painfully recorded, the rest might have a chance to live.

Based on the vividly detailed log entries of Strain and his officers, other period sources, and Balf's own treks in the Darien Gap, this is a rich and utterly compelling historical narrative that will thrill readers who enjoyed In the Heart of the Sea, Isaac's Storm, and other sagas of adventure at the limits of human endurance.