Shy is a 17-year-old Mexican American high school student from Otay Mesa, near San Diego. He works as a towel boy and water boy on a luxury cruise ship to help his family financially following his grandmother's death from Romero Disease. He acutely feels the class divide between the wealthy passengers and the working crew. Despite facing casual disrespect, he remains compassionate, hardworking, and deeply protective of his family and friends.

Carmen is an 18-year-old half-Mexican woman working on the Paradise cruise ship. She comes from a town near Otay Mesa and shares a bond with Shy, as both have lost family members to Romero Disease. She is confident, practical, and engaged to a fiancé waiting for her back home. She handles derogatory comments from privileged passengers with outward ease, ignoring their microaggressions to maintain her professionalism.

Addison is a wealthy teenager traveling on the cruise ship with her father, Jim Miller, and her friend Cassandra. Used to a life of privilege, she initially treats the ship's crew, including Shy, as second-class citizens. Her comfortable world is insulated by money, but she begins asking questions when her father abruptly leaves the ship and takes a strange interest in Shy.

Rodney is a six-foot-four offensive lineman with crooked teeth and a bad haircut. He works as an assistant to the head chef on the cruise ship and dreams of one day becoming a world-renowned chef in New York. He spends his free time reading romance novels and is known among the crew as an enthusiastic hugger who does not quite realize his own strength.

Shoeshine is an enigmatic older Black man who works shining shoes on the cruise ship. He speaks in cryptic warnings and claims that names have no meaning out on the ocean. He pays close attention to the changing weather and seems unusually unfazed by the approaching storm.

William Henry is a loud, larger-than-life Texan oil tycoon traveling in premier class. He plans to propose to his girlfriend during the cruise. He frequently boasts about his wealth and makes casual, racist, and sexist remarks toward the crew, particularly Carmen and Shy, representing the entitled attitudes of the passengers.

Bill is a mysterious man in a black suit traveling on the cruise ship. He actively follows Shy and questions security personnel about him. He wears a suit that appears slightly out of place and makes thinly veiled threats to Shy regarding his interactions with David Williamson, raising Shy's anxiety.

Jim Miller is the wealthy owner of the pharmaceutical company LasoTech and Addison's father. He travels in premier class but takes an unusual, sudden interest in Shy, striking up a conversation and pressing him to join his daughter for dinner. He leaves the ship abruptly on a smaller boat heading for the Hidden Islands.

David Williamson is a middle-aged, balding man who describes himself as a top scientist and co-founder of a business. He approaches Shy in a state of extreme distress, rambling cryptically about betrayal and having blood on his hands. His sudden, tragic action in the book's prologue sets off the central mystery and deeply traumatizes Shy.

Marcus is a hip-hop dancer working on the cruise ship. He is part of Shy's close-knit friend group among the crew. He provides camaraderie and a sense of normalcy for Shy during the stress of catering to the wealthy passengers.

Kevin is an Australian underwear model working alongside Shy. He looks out for his friends and is the first to warn Shy that a strange man in a black suit has been asking questions about him, promising to stay by Shy's side until he is safe.

Cassandra is Addison's friend and travel companion on the cruise ship. Like Addison, she comes from money and joins in mocking the crew members who serve them, viewing Shy's forced politeness as a source of amusement.

Miguel is Shy's young nephew back home in California. Shy loves him like a brother and eagerly gives up his savings to help pay for Miguel's medical care when the boy falls ill with the Romero Disease.

Paolo is the head of security on the cruise ship. He is one of the higher-ranking crew members Shy attempts to track down when he needs answers about the men investigating him.

Supervisor Franco is Shy's manager on the cruise ship. He organizes the crew's efforts to secure the decks when bad weather approaches and holds information regarding the search of Shy's cabin.

Dr. Christian is a recent medical school graduate working on the cruise ship. He assists the crew and passengers when emergencies arise on the vessel.

Toni is a passenger on the luxury cruise. She is focused on her upcoming wedding and represents the ordinary, comfortable lives of the passengers before disaster strikes.