Dr. Heidegger is a man with a profound interest in both science and the occult, or supernatural. He speaks to a bust of Hippocrates, the father of medicine, about his medical cases, but he also keeps a heavy book of spells. He experiments with vacuum tubes and electricity, but he also has friends who know he is interested in mythical curiosities like the fountain of youth. His study is decorated with a full body portrait of Sylvia Ward, his fiancée whom he accidentally killed with an experimental medicine over 50 years ago. Though he has matured somewhat over the years and enjoys the wisdom and position that age has brought him, he has never given up dangerous experimentation. He uses four of his old friends to test the water from the fountain of youth rather than risking it on himself. After watching his friends descend into a stupor of youth, he is glad to have learned he was right. His friends, however, learn nothing and leave to find the source of the water.
Mr. Medbourne squandered his entire fortune in speculation and now, as an old man, lives near the edge of destitution. When he is given the chance to be young again, he immediately begins to concoct wild schemes, such as selling polar ice to India by using whales to tow it.
Colonel Killigrew is a former officer who was both a drunk and a lying flirt in his youth. His years in pursuit of "sinful pleasures" have left him physically ruined, and he is suffering from a number of ailments including gout. As he decreases in age, he immediately begins to eye the Widow Wycherly, keen on renewing their physical relationship.
Mr. Gascoigne was a corrupt politician in his youth. He had a ruinously toxic reputation for a long time but eventually drifted out of public life into obscurity. As he gets his youth back, he begins bombastically quoting meaningless slogans and whispering dangerous slander.
The Widow Wycherly
The Widow Wycherly is a formerly beautiful but still deeply vain woman who had a number of scandalous romances in her youth, including with Mr. Medbourne, Colonel Killigrew, and Mr. Gascoigne. As she becomes younger and returns to her former youthful beauty, she is entranced by herself in the mirror, and she delights in the attention of the men around her. Though the return to age is difficult for all of the characters, the Widow Wycherly seems particularly distraught, which the author seems to attribute to feminine vanity.