Pursued by an Apache war party, buffalo hunter Carter Paxton rides into a medicine cave in Arizona in 1885 and emerges in fifteenth-century England; with him, he brings a Sharps buffalo gun, a Winchester rifle, a pair of Colt six-shooters, and three books that will change the course of history. Within minutes of his advent in 1485, Paxton happens upon a lone hunter under attack by a party of armored men; deciding to even the odds, Paxton gallops into the skirmish with Colts blazing and rescues the solitary man – who proves to be King Richard III. Richard is impressed with Paxton's fighting skills, as well as the sophistication of his firearms, and the two men become fast friends.
Returning to the palace with Richard, Paxton meets Lady Joanna of Warwick, Richard's niece: the chemistry between them is instantaneous and explosive. Later, at dinner, Paxton and Joanna incur the anger of Thomas Stanley and the Duke of Buckingham – Richard’s greatest enemies, now also Paxton and Joanna’s.
Joanna comes to Paxton’s chamber that night, and Paxton confides to her that he knows the history of England – largely from Shakespeare, but also from less-biased historians. He declares his love for her, as well as his determination to prevent Henry Tudor from usurping Richard’s throne.
In the morning, Paxton and Joanna join the king’s hunting party. While in pursuit of a stag, they stumble upon Tudor agent Bishop John Morton passing information to a strong party of Flemish mercenaries; there is a skirmish, in which Paxton uses his Winchester to defeat the Flemings and persuade them to leave Morton behind. Joanna and Paxton turn Morton over to Richard, who orders him hauled off to prison.
With the Battle of Bosworth Field approaching rapidly, Paxton calls upon his knowledge of firearms to create simplified breech-loading rifles and train an elite force of dragoons to use them in battle. Then disaster strikes: Buckingham and Stanley set a trap to kill Richard’s son, Prince Edward. Using Apache interrogation techniques on a captured assassin, Paxton discovers Buckingham’s guilt, pursues him and kills him.
At the End-of-Act-II Crash, not only is the Prince dead, but Queen Anne has fallen into a life-threatening depression, which Paxton cures through a Navajo “Healing Way.” Though still mourning for his son, Richard is now determined to defeat Henry Tudor and the English traitors who support him, at Bosworth Field.
Amidst the chaos of the Battle of Bosworth, Paxton’s elite dragoons wage a desperate action to repulse an attack on Richard’s right flank. At a critical moment, when Stanley is about to lead his troops to Henry Tudor’s side, Paxton kills the traitor with a 1500-yard shot from his Sharps buffalo rifle.
Seeing his imminent defeat, Henry Tudor attempts to escape, but Joanna shoots his horse from under him. Henry must then face Richard in single combat, but while Richard is a consummate fighter, Henry has devoted his life to political intrigue. Henry surrenders, and Richard spares his life at Paxton’s request.
In a final court scene, Richard condemns Henry Tudor to walk the length and breadth of England to learn the people and customs of the nation he would have conquered. Richard rewards Joanna and Paxton by first, agreeing to their marriage, then by giving Paxton the means to finance an expedition to the New World. Fade out on the jubilant couple and a court rejoicing in the promise of peace at long last.