Latimer is an English gentleman with a sensitive and poetic nature, which contrasts sharply with his highly practical family. After suffering a severe illness in Geneva, he begins to experience episodes of insight and foresight, granting him the unwanted ability to read the minds of those around him. His clairvoyant abilities socially isolate him, as he struggles to reconcile the polite manners of Victorian society with the often petty or cruel thoughts he perceives in others. He seeks comfort in the natural world and in literature.

Bertha is an orphan adopted by her aunt, characterized by sharp features, blond hair, and a highly cynical demeanor. She frequently mocks Latimer's poetic sensibilities and fiercely values her own emotional distance. To Latimer, she presents an irresistible mystery because she is the only person whose inner thoughts remain completely hidden from his clairvoyant abilities.

Charles is an orphaned, impoverished English medical student studying in Switzerland. Unattractive and generally excluded from the society of the other boys, he bonds with Latimer over their shared isolation. He is highly focused on his medical theories and ambitious experimental scientific pursuits.

A firm, intensely orderly banker who heavily favors practical pursuits over creative ones. He dictates his youngest son's education toward science and mechanics, actively seeking to suppress his poetic tendencies. He clearly prefers his older son, Alfred, who easily embodies the traditional ideals and social charm expected of an English gentleman.

Alfred is Latimer’s older brother, a handsome and charming man who fulfills the expected social role of an eldest son. He displays a good-humored but self-satisfied nature that deeply frustrates his younger brother. Confident in his social standing, he pursues a standard, polite courtship with their neighbor's niece.

Mrs. Filmore is a neighbor to the Latimer family in England. She adopted her orphaned niece, Bertha, and travels with the Latimers during their European tour. She represents the standard, polite Victorian social circle that surrounds the main families.

Mr. Letherall is a phrenologist hired by Latimer's father. He evaluates the physical shape of the young boy's skull and formally declares him defective in organizational and rational thought. This assessment prompts the family to force Latimer into a strict scientific curriculum.

Mrs. Archer is a working-class maid employed by Bertha. She shares a tense and secretive relationship with her employer, often engaging in hushed arguments. When she falls severely ill, her treatment becomes the subject of a radical medical experiment.