Mortimer is a theater critic who ironically dislikes the theater, regularly writing negative reviews or leaving after the first act. He loves his eccentric family but worries about their history of psychiatric conditions. His grounded perspective shatters when he discovers his seemingly innocent aunts are hiding a dead body in their window seat.

Abby is a sweet, elderly spinster who is viewed as a figure of pure kindness in her Brooklyn community. Underneath her charitable facade, she and her sister maintain a lethal hobby of serving poisoned elderberry wine to lonely old men. She sincerely views this act as a charitable service designed to bring isolated individuals peace.

Martha is the co-matriarch of the Brewster home, operating in total tandem with her sister Abby. She presents herself as a docile, deeply caring woman who takes great pride in her home-cooked meals. She shares her sister's genuinely held, yet entirely absurd, belief that poisoning disadvantaged men is an act of mercy.

Jonathan is Mortimer's estranged brother and a career criminal on the run from the law. He is a calculated killer who frequently uses intimidation to get his way. Thanks to a botched plastic surgery procedure, he bears a striking resemblance to horror actor Boris Karloff—an observation that reliably incites him to physical violence.

Elaine is a sensible, deeply devoted woman who lives next door to the Brewsters. As the daughter of a reverend, she represents a stable, normal life outside the chaotic Brewster bloodline. She cares deeply for Mortimer and wants to support him, even as his behavior becomes erratic and confusing.

Dr. Einstein is an alcoholic plastic surgeon who travels as Jonathan's henchman. His primary responsibility is altering Jonathan's facial features to help him evade police capture, though his inebriated mistakes often cause trouble. He is generally timid and subservient to his criminal partner.

Teddy is Mortimer's brother who lives with his aunts. He operates under the firm belief that he is President Theodore Roosevelt. He harmlessly charges up the stairs, blows his bugle late at night, and unknowingly assists his aunts' criminal endeavors by digging locks for the Panama Canal in the cellar.

Reverend Harper is a local religious leader and Elaine's father. He holds the Brewster sisters in the highest esteem for their apparent charity and community service. He maintains reservations about his daughter dating a theater critic, fearing the influence of the theatrical community.

O'Hara is a Brooklyn police officer who patrols the neighborhood. He is highly oblivious to his surroundings and cares far more about pitching his aspiring play to Mortimer than investigating any suspicious activity in the Brewster home.

Brophy is a local police officer who regularly interacts with the Brewster household. He views the sisters as remarkably warm community members and is completely unaware of the home's violent reality.

Klein is another local police officer who shares Brophy's high opinion of the Brewsters. He is easily irritated by criminals and quick to express disbelief at strange stories.

Rooney is the supervising officer at the local precinct. He is authoritative and quickly dismisses outlandish claims as nonsense, especially when they involve upstanding citizens like the Brewsters.

Mr. Witherspoon is the Superintendent of Happy Dale Sanitarium. He is a dedicated, lonely man who takes his job very seriously, making him an ideal candidate for the Brewster sisters' particular brand of hospitality.

Mr. Hoskins is a lonely older man and the latest victim of the Brewster sisters' poisoned elderberry wine. His body's presence in the living room initiates the main conflict of the story.

Mr. Spenalzo is Jonathan's murdered driver. His body becomes a logistical nightmare as Jonathan and Dr. Einstein desperately try to hide him in the already-occupied Brewster cellar.

Mr. Gibbs is an elderly man with no close family who comes to view the sisters' rental room. He narrowly avoids becoming their next victim thanks to a sudden interruption by Mortimer.