Plot
In 1859, at the San Pedro Valley of Southeastern Territorial Arizona, two separate parties of surveyors mark stakes on opposite sides of the San Pedro River to outline the homestead lots of a forthcoming frontier town, Horizon. Soon after, Desmarais, a missionary, using a "Horizon"-titled single page printed pamphlet poster, seeks out Horizon and discovers all three members of the surveying parties dead at the hands of a Western Apache war band. He buries their bodies and establishes the town of Horizon.
In 1863, American homesteader Horizon faces an Apache raid led by Pionsenay, killing several residents, including Frances Kittredge's husband and son. Russell Ganz, a settlement boy, escapes on horseback to alert the Army at nearby Camp Grant, Arizona. United States Cavalry and Infantry, led by 1st Lt. Gephardt and Sgt. Major Riordan with Chief Scout Neron Chavez, assists with burials, tracks the raiders, and helps survivors. Frances and her daughter Elizabeth seek sanctuary at Camp Gallant. Orphaned Russell joins a posse led by survivor Elias Janney and a scalp-hunter to pursue the Apaches. Gephardt warns the posse against retaliating indiscriminately against uninvolved Natives, motivated by scalping profitability. Frances and Elizabeth adapt to Camp Gallant life. Gephardt's moral stance on indigenous land conflicts with Colonel Houghton's manifest destiny views. Elizabeth befriends troops at the Post, heartbroken when they are recalled to fight in the Civil War. Meanwhile, Frances and Gephardt start a romance.
Pionsenay argues with his tribal elder, Tuayeseh, over his raids on the settlers. Pionsenay believes the settlers will push them out and lead them to war against other tribes, while Tuayeseh believes in co-existence and considers reprisal for Pionsenay's actions. Pionsenay and his warband, including one of Tuayeseh's sons, voluntarily leave the tribe to continue their war against the settlers.
In Montana Territory, Lucy shoots James Sykes and flees to Wyoming Territory with her son Sam. Wounded, Mrs. Sykes orders her sons to recapture them. Now under the name Ellen Harvey, Lucy marries businessman Walter Childs. They live with Marigold, a prostitute. Marigold propositions horse trader Hayes Ellison, then returns to care for Sam while Lucy and Walter go to a land sale. Lucy is horrified to discover the buyers are the pursuing Sykes brothers. Walter is killed by Caleb, and the men kidnap Lucy. Junior sends Caleb to find Sam, who encounters Hayes. In a shootout, Hayes kills Caleb, then flees with Marigold and Sam. They settle in a railroad camp, but Marigold abandons Sam for a gambler, leaving him with a Chinese worker's family.
A wagon train led by Matthew Van Weyden travels from the West Kansas Territory along the Santa Fe Trail to Horizon. Among them are the pretentious British couple Juliette Chesney and Hugh Proctor, who sparked Van Weyden for their lack of commitment in helping out the caravan, along with the extended family of Frances's late husband. They are watched by Pawnee warriors, slowing their progress as they prepare to defend themselves. At night, Juliette catches two men peeping at her while she bathes in the drinking water. Van Weyden gives them a warning, but neither man seems inclined to listen.
Janney discovers Pionsenay as the responsible Apache at a trading post. While Janney and the Trader prevent a confrontation, the group decides to target any Indians for information. They find a Tonto Apache village, wait for the hunters to leave, then attack and kill the tribe's women, children, and elderly. The posse leaves before facing repercussions as their leader, Tracker, kills one of his own men whose failure to tie his horse nearly gave away their positions, with the impact of their actions spreading. Before the film comes to a close, there are montages of clips from Parts 2, 3, and 4 of the Saga while flyers of Horizon are printed from the press.