Ethan Brand is a former lime-burner who left the village eighteen years ago to search for the "Unpardonable Sin." He returns to Mount Greylock claiming to have found it within his own heart. Highly intellectual and deeply isolated, his obsessive pursuit of forbidden knowledge has estranged him from humanity, nature, and God. He maintains a cold, philosophical demeanor that alienates the local villagers who come to see him.

Bartram is a gruff, rugged man who currently operates the lime-kiln that Ethan Brand abandoned years ago. He values hard physical labor and traditional masculinity, showing little patience for anything he cannot readily comprehend. Grounded entirely in practical work, he serves as a foil to his predecessor's obsessive intellectualism and prefers to dismiss strange philosophical ideas as mere madness.

Joe is Bartram's young, sensitive son who helps his father tend the lime-kiln. Unlike his rugged and dismissive father, he possesses a tender spirit and an intuitive understanding of the emotions of others. He is the only person present who genuinely recognizes the bleak loneliness enveloping the returning wayfarer.

The local village doctor is a professional whose life and career have been destroyed by heavy brandy consumption. Despite his own moral failings, he reacts defensively to the returning lime-burner's cold demeanor, ultimately declaring the man insane and completely antisocial.

Lawyer Giles is a former legal professional in the village who now makes his living as a soap-boiler. Like the village doctor, his professional and personal life fell to pieces due to a severe addiction to alcohol. He approaches the returned man with a mixture of terror and curiosity.

Humphrey is an older villager whose daughter left the community to join the circus years ago. He retains a desperate hope for her safety and eagerly questions travelers for any news of her whereabouts.

Esther is Humphrey's missing daughter who left the village to perform as a circus entertainer. During her travels, she crossed paths with the former lime-burner and became the subject of a cold psychological experiment that caused severe damage to her spirit.

This traveling showman carries a diorama from town to town. He recognizes the former lime-burner from their past encounters on the road and mockingly claims to carry the Unpardonable Sin within his wooden box, sparking a hostile physical confrontation.

A local dog provides brief entertainment for the villagers by aggressively pursuing its own short tail. The animal's futile and exhausting task mirrors the obsessive and ultimately pointless intellectual quest of the returning wayfarer.