Anna is an observant and mechanically minded 19-year-old inspecting parts for the battleship Missouri at the Brooklyn Naval Yard. She grew up acting as an accomplice to her father before he vanished when she was fourteen. Driven by a desire for independence, she attempts to break into the exclusively male profession of deep-sea diving. She balances her personal ambitions with her devotion to her disabled younger sister.

Eddie is an Irish-American former stockbroker who lost his fortune in the 1929 stock market crash. Raised in the New York Catholic Protectory after his mother's death, he relies on his wits and discretion to earn a living as a bagman for union bosses and underworld figures. He hungers for a return to financial stability but struggles with severe guilt regarding his disabled daughter.

Dexter is a wealthy nightclub owner and former Prohibition bootlegger operating in a legal gray area. He projects the image of a respectable family man with a mansion and a well-bred wife, though he answers to a powerful mob boss. He uses his suave social manner to maintain his precarious position in the New York underworld.

Lydia is Anna’s younger sister, living with a severe disability that prevents her from walking or speaking clearly. Her daily care places a significant emotional and financial strain on her parents. She responds positively to changes in her environment and sensory experiences like the ocean.

Agnes is a former Follies dancer who left her rural Minnesota home to perform in New York City. She abandoned her entertainment career to become a full-time, devoted caretaker for her disabled daughter. She uses elegant clothing and strict domestic standards to mask her family's poverty.

Brianne is Eddie’s half-sister and a former Follies dancer. She relies on the financial support of various male suitors to maintain her boozy, faded lifestyle. She offers a sharp-tongued but affectionate perspective to the Kerrigan family.

Harriet is Dexter’s wife, born into the old-money Berringer family. She provides her husband with a veneer of upper-class respectability, though her family views him as a criminal outsider. She is highly fashionable but emotionally detached from her husband's struggles.

Tabatha is Dexter and Harriet’s eldest daughter. Raised in extreme wealth and sheltered from her father's criminal activities, she grows into a vain, self-absorbed teenager. Her life revolves around boys, movie stars, and physical appearances.

Lieutenant Axel is a barrel-chested naval officer in charge of training deep-sea divers at the Brooklyn Naval Yard. He holds rigid views regarding the physical and gendered requirements of the military. He attempts to intimidate candidates out of the program with gruff dismissals.

Mr. Voss runs the part-measuring factory where Anna works during the early years of the war. He prizes efficiency and relies heavily on Anna's mechanical precision. His professional appreciation for her work sparks rumors among the other factory women.

Nell is a glamorous, fiercely independent worker at the Naval Yard who befriends Anna. She leverages her peroxide-blonde beauty to navigate wartime New York, prioritizing her own pleasure and financial security. She introduces Anna to the city's lively nightclub scene.

Dunellen is an Irish-American man who grew up in the Catholic Protectory alongside Eddie. He works as a middleman for shady union operations. He employs Eddie for errands but refuses to lend him money directly.

Mr. De Veer is an elderly, wheelchair-bound man with a military past. He recognized Eddie's intelligence during their poker games. He entrusted Eddie with a prized silver pocket watch to keep it safe.

Mr. Q. is a powerful mafioso boss who made his fortune as a Prohibition-era bootlegger. He controls Dexter Styles's legal and illegal operations with an iron grip. He demands absolute loyalty from his subordinates.

Arthur Berringer is Harriet’s father and a representative of old, legitimate New York wealth. He views his son-in-law Dexter with suspicion. He refuses to help Dexter transition entirely into lawful business ventures.

Marle is an African-American candidate in the Naval Yard's deep-sea diving program. He faces significant institutional bias from his instructors. He works quietly and diligently to prove his competence.

Badger is an enforcer working within Dexter Styles's criminal network. He carries out the physical labor of the organization's illegal activities. He operates strictly under orders from higher-ranking mob members.

Rose is one of Anna’s coworkers at the part-measuring factory. She engages heavily in workplace gossip. She views Anna's professional success with suspicion.