Christian Horn is leading his fellow settlers across the desert of the New Mexico Territories in 1847, while his son suffers from fever. He pulls the train to a halt and the other settlers insist they turn back before they die of hunger and thirst. Christian refuses and decides to go a hundred yards over a nearby rim to find what supplies he can. He crosses over the rim, but finds himself confronted by a 20th century highway. He calls back to the settlers, but they've disappeared. He continues down the dune and as he examines the highway, and is almost hit by a truck. Christian throws himself to the side and injures himself when his gun goes off.
Continuing down the road, he comes to a sign saying there's a cafe and gas station a mile ahead. He walks to the cafe and tries to explain to the owner that he saw a monster. The man, Joe, doesn't know what he's talking abot and thinks he's nuts when Chrsitian starts rambling about bringing a wagon train from the East. Joe brings Christian in so his wife Mary Lou can take a look at his injury. He asks about Indians and Mary Lou and Joe joke about the fact there's no hostile ones around. Christian examines the jukebox and the telephone, and Joe asks where he's from. Christian explains he's from Ohio and his people are on the other side of the rim. Mary Lou offers him penicillin and explains it's to ward off infection. He takes the bottle of pills for his son and then notices a calendar with wgaon train on it... and a date of 1961.
Joe and Mary Lou call in the doctor who diagnosis Christian as suffering from malnutrition. Christian has provided a detailed description of his life and has two antique fillings. He suspects that Christian is delusional and calls the sheriff's office. Christian comes out, having discovered an encyclopedia. It has an entry about his son, who grew up to become a doctor specializing in childhood disease and died in 1914. Considering the bottle of penicillin, Christian realizes he's been brought there for a reason. He prepares to leave but the doctor wants him to stay for treatment. Christian barrels his way past Joe and runs down the highway. The sheriff and Joe drive after him and catches up to him as Christian runs up the dune. He stumbles and drops his rifle, then crosses over the rim... and finds himself at the wagon train a few seconds later. He gives the pencillin to his wife to treat their son and notes to Charlie and the others there's a whole lot over the rim a century later.
The sheriff drops Joe off at the cafe, assuring him there's nowhere Christian could have gone and they'll find him. Joe shows Mary Lou the rifle, which has all but fallen apart with a hundred years of age. They wonder who Christian was... and where he came from.