John Mason (40s), has been living in a shack by himself for three months when some men, led by Cochrane, ride up to kill him. He escapes and rides into Grey Falls, Montana, where he saves Ben McClure (mid 30s) from getting killed over a poker game. Both head to Promise, Wyoming, Ben works for John's Dad as a guard on the Pony Express. John hasn't seen his Dad in a long time but they reconcile. Dad and Ben are guarding a train that gets robbed by a masked gang, one of whose members, Rudd Gordon (mid 30s) reluctantly shoots and kills Dad. John rides up but isn't there in time and even gets shot himself for his trouble. With his dying breath his Dad tells John "Dos Equis", meaning double cross, the mark Rudd is tattooed with. John misinterprets this as his Dad wanting him to help Rudd and Alice Gordon (20s), Rudd's sister, who are struggling to keep their Dos Equis Ranch, on which they owe five thousand dollars. John is taken in and cared for by Alice Gordon (20s), who lives on the Dos Equis Ranch with her brother Rudd. Ben plans to propose to Alice, but his engagement ring is stolen during a raid by Rudd's crew of masked men. Cochrane shows up and flashes a marshall's star, he's there to take John away, saying the reward on his head is higher if John's alive. John agrees to go peacefully if Cochrane just gives him a few days. Rudd shoots up Cochrane's gang and tries to pretend their dead bodies are of the crew that robbed the train (which is really his crew). He doesn't realize Cochrane survived. Ben learns that Alice and John have been sleeping together. He still rides out with John on the Pony Express, John has let slip that they are carrying a lot of money (hoping to draw his Dad's killers into the open). Rudd and his crew attack again, Rudd hangs back but John sees him and gives chase. John is caught by Rudd's men and jailed, but eventually Alice breaks him out. They round up a drunken Ben, who out of jealously removes the bullets from John's guns. John tells Ben to take Alice and get out of town, then goes to face Rudd on his own. Rudd is waiting for him with a captured Ben and Alice. John prepares to hand them the money, but they don't see him light a fuse on the bags, which explode. In the chaos that follows Ben gets shot and Rudd holds a gun to Alice's head. All of a sudden Cochrane shows up, explains John found him where Rudd left him for dead and that he's there to arrest Rudd, to avenge the death of his men at Rudd's hands. Ben dies. John informs Alice he kept five thousand dollars of the money for the ranch payment, and they walk off into the sunset.