In which the arrival of reinforcements at Astoria invigorates the establishment’s enterprises, prompting the dispatch of several parties on perilous expeditions, notably one led by the young Robert Stuart entrusted with despatches to New York, amid challenges that include a companion's tragic mental decline and the treacherous navigation of river rapids teeming with opportunistic and hostile natives. The narrative gently follows Stuart’s journey up the Columbia, through scenes of wary negotiations, rattlesnake-infested plains, and warm receptions from equestrian tribes, as they prepare for the daunting trials that lie across the distant Blue Mountains.