Joshua Beck, son of a Virginia plantation owner and his barn slave, flees west in 1821 after his mother dies and he's accused by his white half-brother of killing his father. He ends up in Missouri, where he volunteers for a large trapping party heading north on two keel boats. After saving the Colonel from drowning, he accompanies the land party to barter for horses with the Arikara. When a trapper tries to sneak into the village, the tribe assaults the party with arrows and bullets. While many trappers are killed, Beck saves his friend Moses. He must cross the Missouri River by himself to survive and heads north on foot. Starving, he's rescued by three Crows, Sun Walker and two cousins. After rejoining the land party that the keel boat dropped on shore far above the Arikara, they begin trapping. The Captain is mauled by a grizzly. Beck and Antoine, son of a trapper and a Mandan, search for a comrade and must escape from Pawnee pretending to be friendly. When they climb a tree to hide and sleep, a panther attacks Beck. Although woozy from a poisoned arrow that pierced his butt, he manages to win the battle. Antoine believes Beck will soon be dead and abandons him. By surviving on berries and a bison calf killed by wolves, Beck grows stronger only to meet a party of Sioux. They leave him alone due to his courage proven by the lacerations from the panther's paws. After losing his pants and hatchet to a flooded creek, he's accosted by five Gros Ventre of the prairie. They send a young brave after him in a contest. Jumping into a stream to escape, he's saved by Sun Walker, Storm Cloud and White Bear. Again, they return him to his party. Meanwhile, his half-brother Langford takes over the plantation. More interested in the local tavern and women, he murders an escort's husband, flees, and leaves the bankrupt estate to his mother and twin sister. He heads to Missouri where his uncle, an army Colonel, is stationed. After defeating the Arikara, Colonel Pennington assigns his corporal nephew to build a fort on the site of the former village. Langford soon makes a deal with the British Hudson Bay Company, fierce competitors of American trapping companies, to send furs down to New Orleans and across the Atlantic to quench the European thirst for beaver fur hats. Beck spends a summer at the Crow village where Sun Walker and her cousins live. He learns their language and customs and joins a horse raid against the Blackfoot. Sun Walker, who was brutally raped as a youth by the Blackfoot and has no interest in men, begins to grow fond of Beck, as he's been of her ever since their first meeting. But Beck feels he has a duty to help his land party reach their destination. Back with them, he continues volunteering for dangerous missions as they struggle against fire, malaria, black wolves and hostile tribes on their way to the Mandan villages and Fort Unity. Yet his biggest challenge arises when he unwittingly stops at Langford's fort.