Dr. Heidegger is an eccentric, elderly physician whose odd habits make him the subject of local rumors. He operates out of a gothic, old-fashioned study filled with peculiar artifacts, including a bronze bust of Hippocrates, a closet with a skeleton inside, and a magical leather-bound book. Carrying the grief of losing his partner fifty years ago, he prefers to observe his guests rather than partake in the restorative water himself.

Widow Wycherly is an elderly gentlewoman who lives in deep seclusion due to scandalous stories that ruined her reputation among the local gentry. Once a celebrated beauty, she obsesses over her lost physical attractiveness. She eagerly embraces the chance to see her wrinkles fade and immediately seeks out a mirror to admire her reflection.

Mr. Medbourne is an elderly man who was once a highly prosperous merchant. He lost his fortune through frantic and unwise business speculation, reducing him to near poverty in his old age. When exposed to the restorative water, his mind races back to financial calculations and grand, impractical business schemes.

Colonel Killigrew is an old man whose health is ruined by a lifetime of pursuing sinful pleasures. He suffers from gout and various afflictions of the body and soul. Under the influence of the water, he quickly reverts to his hedonistic tendencies, singing drinking songs and fixing his attention on Widow Wycherly.

Mr. Gascoigne is an elderly, disgraced politician described as a man of evil fame. Time has obscured his past misdeeds, leaving him largely forgotten by the current generation. Given a taste of youth, his mind instantly returns to political maneuvering, uttering loud declarations about patriotism and national glory.

The narrator is the self-conscious storyteller recounting the events of the doctor's experiment. He maintains a playful, slightly ironic tone and admits that he might be the source of some of the exaggerated fables surrounding the doctor. He situates the story in a space between reality and the supernatural.

Sylvia Ward is the doctor's former partner who died fifty years ago on the eve of their wedding. She suffered a slight disorder and passed away after taking one of her partner's prescriptions. Her memory is preserved through her portrait and a withered rose she gave the doctor, which he keeps in his magic book.