Lo is a travel journalist working for a magazine called Velocity. Still traumatized and suffering from insomnia after a recent burglary, she boards the luxury cruise ship Aurora Borealis for what she hopes will be a major career opportunity. She struggles with anxiety and takes medication, causing her to doubt her own perceptions when she hears a splash and suspects a crime has occurred at sea.

Judah is Lo's devoted boyfriend who works as a foreign correspondent, a job that frequently takes him out of the country. He wants a serious commitment and asks Lo to move in with him. He feels guilty for being absent during the break-in at Lo's flat.

A self-made billionaire, Lord Bullmer overcame poverty in his youth to become a massive success in business. He is the wealthy owner of the Aurora Borealis and is hosting its maiden voyage. He projects a stoic, approachable, and charming demeanor to the press and his high-society guests.

A young, dark-haired woman staying in the cabin adjacent to Lo's suite. She lends Lo mascara on the first night but is strangely defensive. Her presence on the ship is an enigma, especially since the crew insists her cabin is entirely empty and unassigned.

Lady Anne is an heiress who provided the financial foundation for her husband's rise in society. She is currently suffering from late-stage breast cancer and undergoing intense medical treatment. Her presence on the cruise surprises some guests given her severe illness.

Camilla is the manager of hospitality aboard the Aurora Borealis. She oversees the ship's staff and ensures the comfort of the elite guests. Her excessively gracious manner covers a strict adherence to the ship's rules and hierarchy.

Cole is a well-known travel journalist and photographer who usually covers political and environmental subjects like the Arctic Circle. He is aboard the Aurora Borealis as a favor to Lord Bullmer. He is forward, flirtatious, and cynical about his own personal life.

Tina is a powerful editor for the Vernean Times. She has a reputation in the journalism industry for being ruthless and stepping on other women to get ahead. Despite this gossip, she is an influential figure on the cruise whom other professionals aim to impress.

Ben is a journalist and a former coworker of Lo's. The two share a complicated romantic history, as Ben broke up with her years ago when she was struggling with severe depression. He is one of the few people on the ship who initially listens to Lo's fears.

Alexander is a well-known food critic and travel journalist. He is physically out of shape and struggles with the physical demands of moving around the ship. He stays up late and observes the nighttime activities of other passengers.

Chloe is an ex-model married to a high-powered financier. She is kind and observant, offering Lo makeup tips to hide her injury. She hints at having past experience with abusive dynamics.

Lars is a wealthy financier and a close associate of Lord Bullmer. He represents the wealthy, patriarchal elite who frequent luxury cruises and dictate social dynamics through financial power.

Owen is a quiet investor who is considering whether to back the Aurora Borealis financially. He keeps mostly to himself but engages in pragmatic conversations about business.

Johann is the head of security aboard the Aurora Borealis. He is responsible for passenger safety but operates with a clear mandate to protect the ship's reputation and Lord Bullmer's interests. He uses Lo's medical history to dismiss her claims.

Iwona is a Polish cleaning woman working on the ship. She speaks limited English and becomes confused when Lo frantically questions her about a missing cosmetic item in an adjacent room.

Ulla is a beautiful, tall front cabin steward. She provides spa treatments and mud wraps to the elite guests. Her striking appearance makes her a focal point for the male passengers on the ship.

Eva is the bubbly spa coordinator aboard the cruise. She tries to accommodate Lo's claustrophobia by offering alternative treatments when Lo panics about going into the lower-deck treatment rooms.

Karla is a chipper steward assigned to serve Lo's cabin. She relies heavily on the income from her job and becomes visibly frightened when Lo questions her about unauthorized passengers on the ship.

Josef is a porter serving the front cabins. He handles guest luggage and engages in a casual romantic liaison with one of the high-profile journalists on board.

Rowan is Lo's demanding boss at the travel magazine Velocity. She is currently on maternity leave, which allows Lo the opportunity to cover this high-profile luxury cruise in her stead.

Lissie is a long-time friend of Lo back in London. She represents Lo's connections to the normal world outside the isolated environment of the cruise.

Solberg is a financier who was originally booked to stay in Cabin 10. He canceled his trip at the very last minute because his passport was stolen during a home invasion, leaving his room supposedly empty.

Konrad is a gentle, elderly farmer living deep in the rural Norwegian fjords. He has a white beard and rheumatic eyes, and despite speaking no English, he tries to communicate safety by showing photos of his grandchildren.