The story begins with old Dr. Heidegger inviting four elderly friends over to his rather eerie study: Colonel Killigrew, Mr. Medbourne, Mr. Gascoigne, and the Widow Wycherly. The four old folks have all fallen a long way from their prime; each squandered his own type of fortune (youth, money, power, beauty) and is now in a miserable state. The narrator also informs us that, when they were young, the three men used to fight over the attention of the Widow Wycherly.
Heidegger's creepy study contains, among other things, a bust of Hippocrates with whom Dr. Heidegger consults from time to time, a magic black book, a skeleton in a closet, and a mirror that supposedly contains the visages of Heidegger's dead patients. The Doctor presents his guests with four empty champagne glasses and an ornate vase full of clear, bubbling liquid. He takes an old, withered rose, drops it into the vase, and shows his guests that it has in fact been rejuvenated to a fresh-blooming flower.
Dr. Heidegger then claims that the liquid in the vase is water from the mythical Fountain of Youth. He would like their help in an experiment: they drink the water, he sits back and watches. The guests are clearly skeptical, but they agree. Before they drink, Dr. Heidegger warns them not to make the same mistakes they did the first time they were young. The guests drink, and they believe they have grown young again. (Whether or not they actually are physically transformed is ambiguous.) Of course, they act like fools, and the three men end up wrestling each other for the Widow's attention. In their tussling they knock over the vase, which spills the elixir all over the floor.
It doesn't take long for the effects of the potion to wear off, and the four guests find that they are old again. Dr. Heidegger does not regret the spilled elixir; he has learned his lesson by watching his guests, and would not drink the water for anything. The guests, however, have learned nothing, and vow to travel to Florida, find the fountain of youth, and drink from it day and night.