Scott plays Capt. Tom Benson of the 7th Cavalry, returning to the fort with his bride-to-be only to find it largely abandoned. He'd been ordered by Gen. Custer, a romantic at heart, to go fetch the lovely lady (Barbara "Della Street" Hale) rather than ride with him to the Little Big Horn. Benson soon learns what he missed, and learns that people hold his luck against him. Many believe that he must have had an inkling of Custer's doom, since everyone now finds the general's foolhardiness obvious, and requested leave out of cowardice. Among those with their suspicions is the officer chairing the court of inquiry into the Little Big Horn debacle, Benson's prospective father-in-law. Benson himself defends his honor and Custer's; he won't accept the likes of Benteen and Reno questioning his hero's tactics, and he'll have no one question his own courage.
To vindicate himself, Benson volunteers for a detail to retrieve the bodies of Custer and the other fallen officers from the battle site. This is asking for trouble, since Sitting Bull's forces now believe that the dead Americans have infused the site with "medicine" that will inspire them to further victories as long as their bodies remain where they fell. Benson complicates his own mission further by recruiting a band of convicts and malcontents who seem ready (the one played by badass specialist Leo Gordon in particular) to frag him at any moment.
A soldier undertaking a perilous mission to refute charges of cowardice can't help reminding me of a better film, Robert Rossen's They Came to Cordura from 1959. The contrasts are drawn more starkly in that picture, in which Gary Cooper must escort a group of Medal of Honor candidates back from Mexico during the expedition against Pancho Villa -- the heroes all proving themselves rather rotten people while Cooper virtually martyrs himself in search of redemption. In 7th Cavalry the Scott character's courage is never really questioned by the audience, and he never really faces the sort of ordeal that would prove his courage beyond doubt to his detractors. In short, he doesn't suffer, apart from taking some lumps in a fistfight with the beefy Gordon. Worse for the theme, Benson owes the accomplishment of his mission not to his own extraordinary bravery but to a deus ex machina contrivance. The late Harry Carey Jr. arrives at the fort and announces himself as an eyewitness to Custer's order to Benson. He can vindicate Benson on the spot, but rather than do something practical like give a deposition to the court of inquiry, he rides out to find Benson. Along the way, an Indian kills him but fails to capture Carey's horse. This beast happens to be Custer's second-favorite steed, which makes its way to the Little Big Horn, where Benson's little crew is surrounded by Sioux warriors. Sitting Bull thinks it'd be wrong to shed more blood at the battle site, but has nothing against starving the bluecoats by trapping them there. Leo Gordon tries to break through the cordon, passes through and gets an arrow in his back. It looks bad for our hero until the horse arrives. Somehow the Sioux recognize this as Custer's horse, and take it to be the ghost of the horse he rode in on. They interpret its appearance as a confirmation that the bluecoats should take the body of "Long Hair" home after all, so they leave.
Lewis supposedly had qualms about the historical accuracy of the story; whether he expressed them to Scott, who was co-producer of the film with his usual partner Harry Joe Brown, is unclear, as is whether this has anything to do with Lewis never working with Scott again. The actor may simply have preferred Boetticher after doing Seven Men From Now with him for John Wayne's production company that same year. It's worth noting that Scott and Boetticher avoided subjects on the scale of 7th Cavalry, and did nothing nearly as silly. Lewis's film remains visually impressive but the screenplay's already-outmoded (?) reverence toward Custer and its patronizing attitude toward Native superstition leave it with the old-fashioned formula westerns that Randolph Scott belatedly and triumphantly outgrew.