The Virginian makes the acquaintance of a young man, Mark Shannon (Richard Beymer), who along with his sister (Diana Lynn) and her love interest, trail boss Jack Slauson (Myron Healey), is taking a cattle herd to the army. When near Medicine Bow it is learned the Shannon herd could be carrying Spanish fever. Those cattle are largely immune but the local cattle are not. The local ranchers, with the Virginian acting as their delegate, try to get the herd to bypass the Medicine Bow area. By taking another, but more direct, route, the herd would avoid infecting the local cattle. However,there would be substantial losses to the Shannon herd because of a drought affecting the other route. Mark refuses and this leads to a showdown not only with the Virginian and Medicine Bow ranchers but also with Slauson.
