Hazel is a 12-year-old English girl traveling to New York to work in a garment factory and send money back to her struggling family. Unable to afford a boarding ticket, she hides in a luggage trunk to stow away in the ship's cargo bay. Driven by an intense curiosity and a desire to become a journalist, she boldly explores the Titanic, taking notes on its design flaws and safety issues. She questions authority figures directly and completely ignores the strict social boundaries that separate the passenger classes.

Charlie is a young porter working as part of the Titanic's crew. Like Hazel, he works constantly to send his wages back home to his large family in England. He takes deep pride in his job and initially prioritizes the ship's reputation over its mechanical flaws. After discovering Hazel stowing away, he secretly provides her with an empty cabin and food, establishing a strong bond with her.

Mrs. Abelman is an elderly passenger traveling alone on the Titanic. Having lived in both poverty and extreme wealth throughout her life, she completely ignores the ship's strict class segregation rules and goes wherever she pleases. She recognizes Hazel's intelligence immediately and gives her a leather notebook to support her dream of becoming a journalist. She serves as a wise, encouraging guide who shares her knowledge of ocean science and human nature.

Sylvia is a first-class passenger around Hazel's age traveling to New York with her governess. She is somewhat sheltered from the world but eager for friendship, happily ignoring Hazel's ragged clothing and lack of luggage. Sylvia invites Hazel into the luxurious spaces of the ship, offering her expensive clothing and companionship, though she occasionally struggles to understand the harsh financial realities of Hazel's life.

Mr. Mollison is a first-class passenger traveling with his wife. He presents a superficial air of extreme wealth but spends his time planning illicit schemes to cheat other passengers out of their money. He frequents the ship's gambling tables, using dishonest methods and psychological manipulation to win against vulnerable targets.

Mrs. Mollison travels in first class with her husband but harbors a hidden history as a former housekeeper who forcefully worked her way into wealth. She is sharp-tongued, highly defensive of her social standing, and deeply hostile toward Hazel. She actively plots to steal money and documents from other passengers and works continuously to suppress Hazel's investigative writing.

Miss Gruber is Sylvia's strict governess, tasked with managing the young girl's education, etiquette, and social behavior. Having grown up in poverty herself, she abandoned her early dreams of becoming a cartographer and now firmly believes that people should not aspire beyond their assigned social station. She heavily disapproves of Hazel crossing into first-class areas and frequently attempts to separate the two girls.

Captain Edward Smith is the commanding officer of the Titanic. He projects absolute confidence in his massive vessel, assuring worried passengers that the ship is entirely safe and that the lookout crew will spot any oceanic dangers. He maintains a calm exterior, even as he receives repeated ice warnings via telegraph from other ships in the area.

Mr. Waddington is a young engineering student studying ship design. He engages politely with Hazel's technical questions about the Titanic, explaining the function of watertight bulkheads and the potential risks of a direct iceberg collision. He provides Hazel with critical knowledge about the ship's structural vulnerabilities.

Mr. Ismay is the wealthy owner of the White Star Line and the Titanic. He travels on the ship's maiden voyage to witness its anticipated success firsthand. He holds significant influence over the ship's operations, occasionally reviewing important telegraph messages before they are shared with the broader navigation crew.

Hazel's mother is a widow struggling to raise five children in England after her husband died tragically in a fishing accident. The intense financial pressure on her household forces her to send Hazel to America. Her pragmatic views on wealth and survival frequently echo in Hazel's thoughts.