"It's been said that science fiction and fantasy are two different things: science fiction, the improbable made possible; fantasy, the impossible made probable. What would you have if you put these two different things together? Well, you'd have an old man named Ben who knows a lot of tricks most people don't know and a little girl named Jenny who loves him - and a journey into the heart of the Twilight Zone."
The story opens at a public park, where a group of children are playing softball. They are accompanied by Old Ben, a kindly, grandfatherly gentleman, whom the kids adore. When it is Old Ben's turn at bat, he hits the ball in close to his hands, but the ball carries over the fence and out of sight, ending the game. They then decide to play "Spaceman", one of their favorite games. Old Ben, who usually plays the spaceman, suggests that Jenny play the visitor from outer space this time. Jenny declines, saying she can't make herself into as convincing a spaceman as Old Ben, so Old Ben assumes his customary role. He runs behind a huge tree to prepare.
When Old Ben emerges (looking like a nightmarish, shelled monster), the children "zap" him with pretend guns, and Old Ben fakes his death and stumbles back behind the tree. Old Ben then reappears from behind the tree in human form and announces that the spaceman is gone, and the camera then pans to Rod Serling seated on a park bench as he introduces this episode, noting that it combines science fiction ("the improbable made possible") with fantasy ("the impossible made probable").
Old Ben carries Jenny home (she walks with a leg brace that restricts her movement), where she lives with her abrasively unsympathetic aunt, Agnes Gann. As they approach the rowhouse, Ben causes his roller skates to dematerialize. This phenomenon is observed by two well-dressed men who are watching the house from across the street.
The two men enter the apartment building and question Agnes about Ben. Agnes is not surprised, assuming the police are interested in Ben. She believes him to be of questionable character. Jenny, who has been sent to bed without supper for spending time with Old Ben, overhears the conversation and limps upstairs to Old Ben's apartment to warn him about the two men. Old Ben lets Jenny in on his secret that he is actually from another planet, a planet Jenny has never heard of, and that his appearance is only a disguise. Old Ben decides it's time for him to "skedaddle" again, but before departing he uses a strange device to heal Jenny's leg. The two strangers meet Jenny walking down the stairs without her brace. The plot thickens as the men use a device identical to Old Ben's to make Jenny temporarily deathly ill, forcing Ben to return and save her.
Old Ben comes back to Jenny's room and makes her well again. As she thanks him, she sees the two men watching Old Ben. They begin addressing him as "Your majesty." Old Ben explains to Jenny that he is not a criminal but the king of his planet. He grew weary from the pressures of ruling his world, from having so much of his authority overridden by red tape...and by "the Council". Accordingly, Ben came to Earth for a self-authorized vacation. The strangers tell Jenny that Old Ben's people love him as much as she does; they want him to return and continue the remainder of his 5,000-year reign. Old Ben knows he must go back to his planet, but regrets that it would be against the rules for Jenny to go with him. Old Ben is granted a moment alone with Jenny to say goodbye after he promises not to run away.
Jenny comes up with a plan that will keep them together. She has Ben change himself into her identical twin. Since Old Ben's subjects are unable to tell them apart, they are forced to return with both of them.
At the end of the episode, host Rod Serling holds up an 8-by-10 black-and-white photograph of a handsome young man, noting that the photo shows Old Ben's true appearance and that when Jenny grows up, she will become his queen.
"Mrs. Gann will be in for a big surprise when she finds this under Jenny's pillow, because Mrs. Gann has more temper than imagination. She'll never dream that this is a picture of Old Ben, as he really looks, and it will never occur to her that eventually her niece will grow up to be an honest-to-goodness queen - somewhere in The Twilight Zone."