The 19-year-old heir to the Scarlet Gang, Juliette recently returned to Shanghai after spending four years in New York. She cultivates a ruthless, fashionable exterior, favoring Western flapper dresses and concealing weapons on her person to project strength. Her brash and impulsive demeanor serves as armor to protect her from the trauma of her past and to secure her position as the future leader of her family's criminal empire.

The Russian heir to the White Flowers gang, Roma is Juliette's former romantic partner and current rival. Unlike many in his family, he dislikes violence and employs it only as a last resort, preferring an analytical and scientific approach to problems. He carries the heavy burden of his father's harsh expectations and deeply regrets the bloody feud between his gang and the Scarlet Gang.

Lord Cai's niece and Juliette’s trusted friend, Kathleen works as an assistant and spy for her cousin. A pacifist who despises the gang violence destroying Shanghai, she prefers pragmatic, step-by-step solutions to conflict. She relies on Juliette for protection and remains fiercely loyal in return, often acting as the heir's conscience.

Roma's cousin and one of his few openly loyal allies within the White Flowers. Benedikt is thoughtful, sensitive, and highly observant, often fixating on specific routines or minute details. He works closely with his roommate Marshall to track down the source of the madness spreading through the city.

A Korean member of the White Flowers and Roma's steadfast friend. Marshall is an energetic jokester who speaks multiple languages and uses humor to mask his sharp intellect. Because he is not tied by blood to the Montagov family, he feels more loyalty to Roma personally than to the gang's ongoing feud.

A handsome British expatriate and the son of trader Walter Dexter. Paul represents the foreign capitalist interests seeking to profit from Shanghai's booming economy. He acts entitled and pursues Juliette romantically, persisting even when she rejects his advances and involving himself in the city's political conflicts.

Juliette’s impulsive and quick-tempered cousin. Tyler constantly seeks to undermine Juliette and usurp her position as the heir to the Scarlet Gang. He believes violence is the primary solution to any problem and possesses a fragile ego that relies on the validation of his gang subordinates.

Roma's 12-year-old sister. She is curious and frequently spies on adults to gather information for the White Flowers. Her involvement in the gang's business puts her in direct danger as the sickness spreads through the city streets.

Juliette and Kathleen's cousin. Rosalind works as a dancer in Scarlet Gang territory and tries to survive the escalating violence in Shanghai. She occasionally assists Juliette with gathering information but prefers to avoid direct involvement in assassinations or gang warfare.

The leader of the Scarlet Gang and Juliette's father. He runs his criminal empire with a traditionalist mindset, favoring manpower over modern technology. He places immense pressure on his daughter to prove her strength and prioritizes the threat of Communism over the mysterious deaths at the port.

The leader of the White Flowers gang. He demands perfection from his subordinates and shows open disappointment in Roma's reluctance to use violence. He dismisses early warnings about the monster, preferring to blame the rival gang or political factions for the city's troubles.

Juliette's mother and a senior figure in the Scarlet Gang. She maintains a calm, collected demeanor even when violence breaks out inside her own home. She pushes Juliette to secure political alliances with the French to maintain the gang's dominance in Shanghai.

A British trader operating in Shanghai. He approaches the Scarlet Gang with a proposition to sell a new opioid called lernicrom, representing the ongoing exploitation of the city by foreign colonial powers.

The head scientist for the White Flowers. He operates a modern, secret laboratory where he manufactures drugs and studies the physical evidence left behind by the madness.

The Secretary-General of the Communist Party in Shanghai. Gang leaders rumor that he controls the monster spreading the sickness, making him a primary target for both the Scarlet Gang and the White Flowers.

The personal assistant to Communist leader Zhang Gutai. He manages access to his boss and guards the apartment against suspicious visitors.

A violent and ambitious member of the White Flowers. He views himself as a rival to Roma and frequently disobeys orders to indulge his aggressive impulses in the underground fighting rings.

A contact who picks up deliveries for the mysterious Larkspur figure. He trades information for alcohol when cornered by gang members seeking answers about the vaccine.