Vera is a former games mistress now employed as a secretary on Soldier Island. Intelligent and observant, she is the only one to draw connections with the "Ten Little Soldier Boys" nursery rhyme. Despite her sharp mind, Vera is haunted by her past actions and is prone to hysteria.

Lombard is a charismatic, skilled man with a mysterious past and a strong instinct for self-preservation. He is often described with wolf-like features, giving him a dangerous and predatory edge. Known for carrying a revolver, he is clever and resourceful.

Blore is a former corrupt police officer and private investigator. He is self-serving and suspects various guests throughout the novel. Though physically strong, his clumsy nature and frequent change of opinions about who the murderer might be are notable.

Dr. Armstrong is a successful doctor and recovering alcoholic. His past mistake of operating while drunk haunts him, but he holds a certain naïveté, making him trust those he shouldn't. His disappearance significantly heightens the suspense in the narrative.

Emily Brent is a rigid, self-righteous woman who intensely adheres to her religious beliefs to justify her actions. She is described as having an unyielding sense of morality and lacks remorse for past actions, despite signs that they linger in her conscience.

Mr. Rogers is a professional and competent butler hired to work on Soldier Island. Along with his wife, he is implicated in a former crime involving the death of an elderly woman. He appears respectable but holds darker secrets regarding his past actions.

General Macarthur is an elderly soldier haunted by his conscience over sending his wife’s lover to his death. He lives with intense paranoia and guilt, resigning himself to isolation on the island, experiencing peace with the idea of death.

Mrs. Rogers works as a housekeeper on the island alongside her husband. Her demeanor is described as ghost-like and fearful, likely due to a guilty conscience related to her involvement in a past crime. Her presence contributes to recurring themes of gender bias in the narrative.

Anthony Marston is the youngest guest on Soldier Island, characterized by his carefree, amoral nature. His lack of concern for others is noted, especially after a fatal accident he was involved in. He plays a key role in initiating the story's conflict.