We begin with a scene where a roadside mechanic is changing the tire on a young lady's car.  Serling begins his narration: "Her name is Nan Adams.  She's twenty-seven years old.  Her occupation: buyer at a New York department store, at present on vacation, driving cross-country to Los Angeles, California, from Manhattan....".  In our scene, the mechanic tells Nan that she is lucky to have survived the tire blow-out, given the speed she was traveling, and that instead of calling a mechanic, someone may have been calling for a hearse.  Serling continues the narration:  "Minor incident on Highway 11 in Pennsylvania, perhaps to be filed away under accidents you walk away from.  But from this moment on, Nan Adam's companion on a trip to California will be terror; her route--fear; her destination--quite unknown."  At this point, Nan gets her first glimpse of the hitchhiker at the blow-out scene.

At a service station, she sees the hitchhiker again, the same man, and is visibly disturbed.  She mentions it to the mechanic, but he doesn't see any hitchhiker.  Fifty miles down the road, and then again even further along the way, she sees the same man.  Now he is always ahead of her and seemingly at every stop she makes.  By now she is starting to get freaked out.

At a turnpike diner, she asks about the prevalence of hitchhikers in the area, only to be told that they are rarely found on the turnpike.  At one point she is stopped due to road construction, where she is approached by the hitchhiker who inquires if she is heading west.  She freaks and drives around the construction barriers.  She next pulls up to some railroad tracks, barrier lights flashing, train bearing down.  She sees the hitchhiker, pulls ahead, and stalls on the tracks.  She manages to back off the tracks in the nick of time as the train speeds by.  Now the hitchhiker is gone.  She is terrified and surmises that he wants her to die.

On the fourth day of her trip, in New Mexico, she takes a side road in an effort to elude the hitchhiker.  Late at night, she runs out of gas.  She walks to a gas station just up the road but is refused service due to the lateness of the hour.  A sailor, returning to San Diego from leave, happens by.  Nan offers to drive him to his base, and in return he gets the needed gas.  In their conversation she tries to logically conclude how she can keep seeing the same man over and over again.  Perhaps it happens if she drives at a steady speed while he gets rides in faster vehicles.  As they travel on, she continues to see the hitchhiker and tries to run him over several times.  The sailor doesn't see him (of course), and after a near accident, he leaves, deciding he would be safer in finding another way to get to San Diego. 

Arriving in Tucson, Nan decides to call home to seek reassurance.  Instead of her mother, a Mrs. Whitney answers the phone.  She explains that Mrs. Adams is in the hospital suffering from a nervous breakdown.  She tells Nan that it all came on very suddenly after Mrs. Adams learned about the death of her daughter, killed six days ago in a traffic accident on a Pennsylvania highway.

Now it all makes sense.  Nan is no longer afraid.  She realizes that she is dead, and that the hitchhiker is death personified.  She gets back into the car, and in her vanity mirror sees the hitchhiker, who asks, "I believe you're going my way?"

Serling then ends with the following: "Nan Adams, age twenty-seven.  She was driving to California, to Los Angeles.  She didn't make it.  There was a detour--through the Twilight Zone."