"In this corner of the universe, a prizefighter named Bolie Jackson, one hundred and eighty-three pounds and an hour and a half away from a comeback at St. Nick's Arena. Mr. Bolie Jackson, who, by the standards of his profession is an aging, over-the-hill relic of what was, and who now sees a reflection of a man who has left too many pieces of his youth in too many stadiums for too many years before too many screaming people. Mr. Bolie Jackson, who might do well to look for some gentle magic in the hard-surfaced glass that stares back at him." - Rod Serling, opening narration.

The following synopsis comes care of Wikipedia.org:

Bolie Jackson is a washed-up boxer who accidentally breaks the knuckles of his hand right before his big comeback fight. He is knocked down and just about to be counted out when he suddenly, magically switches places with the other boxer. Bolie is now standing over his vanquished opponent who is now the one laying on the canvas being counted out.

Bolie celebrates his victory without even a trace of his broken hand. He doesn’t understand what happened. He remembers being knocked down, being unable to get up, knowing he was about to be counted out. He has no memory of getting back up to win the fight, nor can he figure out why his previously broken knuckles feel fine. However when he mentions being knocked down to his manager, his manager tells Bolie that he must be crazy, that he was never knocked down at all. Bolie can think of no explanation so he attributes his memories to being some sort of strange dream. He doesn’t remember how he achieved his great victory, but he is all too happy to believe in it when he is told how brilliantly he fought. He figures his knuckles must have only been bruised, not broken, after all.

However, there is one other person besides Bolie who does remember Bolie being knocked down and about to be counted out. That person is young Henry, the son of Bolie’s neighbor. And he has an explanation for what happened that reversed that fate. Specifically, Henry tells Bolie that he, Henry, has the power to make a wish and have it come true. And that he had used the biggest, tallest wish he could come up with for Bolie. Henry says that as Bolie lay there on the canvas, about to be counted out, Henry wished that it was the other fighter who had been beaten and that Bolie were the victor. He wished as hard as he possibly could and thus the wish came true.

Bolie can’t accept this. He says he doesn’t believe in the power of a wish. That belief is for children, not adults. He insists that whether he remembers it or not, he must have simply fought a great fight and that’s all there is to it. Henry warns Bolie that the only way the wish can have its power is if you believe in it. If Bolie doesn’t believe, the wish will not be true.

But ultimately Bolie is unswayed. He cannot summon enough childhood spirit within himself to believe in wishes. He finally and fully rejects that a wish could have had anything to do with what happened. And as soon as he does so, time is reversed. We are back to where we started, with Bolie laying on the canvas, and the other fighter standing over him. This time the referee finishes counting Bolie out. He has lost the fight. His broken knuckles are very much and very painfully present and accounted for.

No one has any memory of the alternate history in which Bolie was the victor. Henry remembers making the biggest wish he possibly could for Bolie as Bolie was lying there on the canvas, but obviously the wish didn’t work. So he declares with resignation that he won’t be making any more wishes. He no longer believes in their power. And so Henry has lost this magic of his youth, and has become just like all the rest of us.

"Mr. Bolie Jackson, a hundred and eighty-three pounds, who left a second chance lying in a heap on a rosin-splattered canvas at St. Nick's Arena. Mr. Bolie Jackson, who shares the most common ailment of all men, the strange and perverse disinclination to believe in a miracle, the kind of miracle to come from the mind of a little boy, perhaps only to be found in the Twilight Zone." - Rod Serling, closing narration.