Lord Arthur is a wealthy, charming young aristocrat engaged to the beautiful Sybil Merton. Following a palm reading, he becomes convinced that he must commit a serious crime before he can marry. He approaches this perceived duty with methodical, misplaced common sense, consulting toxicology books and exploring dangerous circles in London to fulfill his fate.

Lady Windermere is a wealthy society hostess known for her clever epigrams and carefully curated parties. She views pseudosciences, such as palmistry and telepathy, as amusing forms of light entertainment rather than serious guides for living. Her arch tone and reliance on appearances reflect the broader values of her upper-class social circle.

Mr. Septimus R. Podgers is a professional cheiromantist who provides entertainment for the upper classes. Though he lacks the mysterious or esoteric appearance expected of his profession, his talent for reading palms fascinates his wealthy clients. He is socially inferior to the aristocrats he entertains and sometimes crosses the line into indiscretion during his readings.

Sybil is Lord Arthur's beautiful fiancé, characterized by her exquisite appearance and devotion to her future husband. She stands somewhat outside the artificial social world inhabited by Lady Windermere. She waits for Lord Arthur as he repeatedly postpones their wedding to resolve what he calls a "terrible difficulty," accommodating his shifting schedules despite her own distress.

Lady Clementina is a sweet, elderly woman and a distant relative of Lord Arthur. She suffers from frequent bouts of heartburn and welcomes the company of her younger family members. She gladly accepts a silver bonbonnière from Lord Arthur, believing it contains medicine for her ailments.

The Dean is Lord Arthur's uncle and a prominent church figure. He is a family man who lives with his daughters. Lord Arthur arranges for an anonymous, mechanical package to be sent to the Dean's home.

Count Rouvaloff is a Russian aristocrat who effortlessly blends into London high society. Behind his respectable exterior, he operates as an agent with connections to radical political groups. He acts as a liaison for Lord Arthur when the young man needs specialized, dangerous equipment.

Herr Winckelkopf is an explosives expert and conspirator who operates from a seedy street but maintains refined tastes. Despite his criminal profession, he possesses excellent manners and recognizes members of high society from attending the same parties.

The Duchess is an aristocratic friend of Lady Windermere. She initially expresses reluctance to participate in the parlor games, warning against tempting fate. However, she easily changes her mind after receiving a flattering prediction about living a long, happy life.

Jane is the daughter of the Dean of Chichester and Lord Arthur's cousin. She writes lively letters to her extended family. She is easily amused by novelties and assumes that minor domestic disturbances are simply fashionable city trends.

Mr. Pestle is a toxicologist who supplies dangerous chemicals from his shop. He briefly questions Lord Arthur's request for a large dose of aconitine. He quickly drops his concerns when Lord Arthur provides a simple, practical excuse about needing to put down a large dog.

Lady Fermor is an aristocratic partygoer who participates in the entertainment at Lady Windermere's opening party. Her private preferences are uncomfortably exposed by Mr. Podgers during a public palm reading. Her embarrassment demonstrates the social risks of the palmist's lack of discretion.

Lord Arthur's unnamed brother is an aristocrat who enjoys luxurious travel. He accompanies Lord Arthur on a two-week trip to Venice. He notices his brother's nervous behavior and attempts to distract him by suggesting an excursion to Ravenna.

An aristocratic matriarch who corresponds with her extended family. She receives letters from her niece Jane about the events in Chichester. She finds herself confused by her son's sudden dismay over seemingly harmless family anecdotes.

A gentleman who receives a "manly" letter from Lord Arthur explaining the need for a wedding postponement. Along with his wife, he begins to question the reliability of his daughter's fiancé as the delays continue to mount.