Holmes is a private investigator who possesses a genetic hyperosmic sense of smell, allowing him to perceive unusually detailed scents. He relies on heroin to dull this overwhelming sensory input and to manage his severe panic attacks. He holds a sharp intellect and a purposefully antagonistic attitude toward those he dislikes, frequently using his deduction skills to annoy authority figures.

Poe is a charming, flirtatious private investigator who frequently drives fast sports cars. He struggles with heavy alcohol consumption, utilizing it as a coping mechanism for the profound grief he carries over the death of his former romantic partner. More physically engaged than his colleagues, he typically leads the chases and physical confrontations required during their cases.

Marple is an observant and empathetic private investigator who serves as the emotional core of the firm. She possesses a keen understanding of human nature and connects easily with crime victims, offering them comfort and support. She utilizes an impressive grasp of legal knowledge to protect her firm from police interference.

Grey is a detective lieutenant with the New York Police Department who initially approaches the new private investigators with heavy skepticism. She grows increasingly intrigued by their unorthodox methods and begins feeding them high-profile cases. She balances her strict adherence to police protocol with a growing personal and professional loyalty to the investigative trio.

Boolin is the police commissioner of New York City and a staunch opponent of private investigators. He possesses a strong faith in the established structures of policing and political power. He deeply resents Holmes, Marple, and Poe for showing up his department and frequently tries to force them under NYPD control using threats of arrest.

Rollins is the mayor of New York City who finds himself embroiled in controversy when a young woman he knows goes missing. He is a powerful political figure who relies heavily on his connections and wealth to maintain his authority in the city. He views the private investigators as a severe threat to his administration.

Bain is a billionaire CEO and a major financial donor to both the mayor and the NYPD. He demands complete discretion regarding the theft of his priceless antique books. He exhibits a highly self-important demeanor and frequently clashes with the detectives over their expensive fees and investigative methods.

Addilyn is a wealthy woman who hires the detectives when her daughter, Zozi, and second husband, Eton, vanish. She is highly anxious and relies heavily on Marple's comforting presence to navigate the terrifying prospect of a kidnapping and the subsequent ransom demands.

Eton is a wealthy businessman and Addilyn's second husband. He disappears alongside his stepdaughter, Zozi, prompting a massive search by both private investigators and federal authorities. He is initially believed to be the victim of a cartel kidnapping.

Zozi is an 18-year-old private school student who goes missing alongside her stepfather, Eton, and her dog, Toby. Described by her classmates as a "campus hero," she is the subject of a high-stakes ransom demand that brings federal agents into the investigation.

Virginia is a young, efficient worker whom Poe hires away from an animal shelter to serve as the assistant for Holmes, Marple & Poe Investigations. She quickly becomes indispensable to the firm, managing their security codes, organizing their space, and providing valuable sensory insights regarding the building's history.

Kristin is a special assistant to Mayor Rollins. She acts as a strict gatekeeper for the city's political elite and becomes deeply entangled in the investigation of Sloane Stone's disappearance.

Sloane is a young Black attorney described as a "Brooklyn girl made good." Her sudden disappearance draws intense media and police attention, prompting the private detectives to investigate her case to prove their skills.

Lucy is a young woman who relocates from rural Texas to New York City to pursue a modeling career. She quickly impresses agencies with her skills but begins receiving anonymous, threatening text messages.

Luka is a successful art thief who uses complex methods to steal masterpieces. He enjoys the challenge of finding buyers for stolen goods and becomes a target for the detectives' investigation into the stolen literary manuscripts.

Blythe is an FBI agent who specializes in art theft. He operates a team of master art forgers who create replicas to catch criminals attempting to launder money through art sales.

Stans is an FBI agent who assumes control of the Charles kidnapping investigation. She coordinates ransom drops and manages the federal response to the crisis, often clashing with the private detectives over jurisdiction and tactics.

Richard is independently wealthy after selling his family's funeral home. He and his brother Nelson live in a large house equipped with industrial air purifiers, hidden compartments, and an elaborate setup for processing chemicals.

Nelson shares his brother's highly secretive life in their heavily modified home. He helps manage the complex systems running within the property and engages in violent confrontations when intruders discover their secrets.

Carson is Lucy Ferry's ex-boyfriend who follows her from rural Texas to New York City. He drives a white pickup truck with a Texas lone star decal and severely struggles to accept the end of their relationship.

Mary was an Irish 19-year-old immigrant who worked overnight in a Brooklyn bakery before her unsolved murder in 1954. Her decades-old cold case captivates Marple's attention and haunts the building the detectives purchase.

Annie is Poe's late romantic partner. Her memory profoundly affects Poe, driving his alcohol consumption and his habit of collecting classic sports cars manufactured in her birth year.

Darla is a private school student and a classmate of Zozi Turner. She views Zozi as a "campus hero" and becomes deeply involved in the complex events surrounding Zozi's sudden disappearance.

Gretchen is a real estate agent trying to sell a difficult commercial property. She is astonished by the famous literary names of the three detectives who arrive at the last minute to purchase the building.

Raymond is Grey's contact with ties to the CIA. He uses his intelligence network to quietly investigate the mysterious backgrounds of Holmes, Marple, and Poe, uncovering strange anomalies in their records.