Erin is a documentary filmmaker in her early thirties working on a project interviewing convicts shortly before and after their prison releases. She lives a comfortable, upper-middle-class life in London with her fiancé, Mark. When she and Mark discover a mysterious duffle bag while honeymooning in Bora Bora, her life takes a sharp turn into deception and illegal activity. She often acts as a people-pleaser but begins to exhibit more independent, sometimes reckless decision-making as the pressure of hiding their discovery mounts.

Mark is Erin's fiancé and the primary breadwinner for their household, working as an investment banker specializing in sovereign debt. His sense of self-worth is deeply tied to his financial success and his ability to provide a luxurious lifestyle. When he unexpectedly loses his job just before their wedding, he struggles to cope with the perceived failure. Finding the mysterious bag on their honeymoon offers him a seemingly easy path to regain his financial standing.

Eddie is a former East London crime boss currently serving a seven-year sentence for money laundering at Penton Prison. He serves as one of the three subjects in Erin's documentary. Despite his criminal background, he maintains a polite, composed demeanor and retains significant connections to the outside world, managing to keep tabs on Erin's personal life from behind bars.

Alexa is an inmate who has served nearly two decades for assisting in her mother's willing suicide. As her release date approaches, she maintains a calm, self-possessed attitude that contrasts sharply with her environment. Her primary goal upon leaving prison is to start a family, a desire that deeply resonates with Erin's own aspirations.

Holli is a twenty-three-year-old woman serving time for arson after setting a bus on fire during the London Riots. Though she attempts to present herself as reformed to the camera, she clearly thrives on the thrill of her crimes. Her ability to instantly shift her demeanor from a hardened criminal to a prim, normal young woman deeply unsettles Erin.

Andy is a Detective Chief Inspector who becomes involved in Erin's life through her documentary work. He possesses an easy confidence and charm that he uses to ingratiate himself with people during his investigations. His presence introduces a significant complication for Erin, who is desperate to avoid any police scrutiny regarding the duffle bag.

Patrick initially presents himself as a friendly prison employee who stops Erin to ask about her documentary work. His failure to provide a surname and the discrepancies in his story quickly trigger Erin's suspicions. He represents a source of growing paranoia for Erin, who fears he might be connected to the downed plane.

Caro is an affluent friend of Erin who lives a carefree, upper-middle-class lifestyle. She represents the social circle Erin belonged to before Mark's job loss introduced severe financial anxiety. Their relationship proves somewhat shallow when Erin attempts to seek meaningful advice and comfort regarding her fiancé's unemployment.

Lottie is the estranged daughter of Eddie Bishop. She has spent years trying to protect herself and her own family from the dangerous reality of her father's criminal past. When Erin approaches her with a recorded message from Eddie, Lottie must weigh her lingering love for her father against her need for safety.

Sally is a British tourist vacationing at the same luxury resort as Erin and Mark. She and her husband cross paths with the newlywed couple, establishing a brief, friendly vacation acquaintance. News of her sudden involvement in a suspicious scuba diving accident deeply impacts Erin's state of mind.

Daniel is vacationing with his wife, Sally, in Bora Bora. He shares a brief acquaintance with Erin and Mark before a tragic and suspicious scuba diving accident turns him into a source of immense anxiety for Erin. She fears the incident is connected to the mysterious duffle bag they found.

Hector is a professional associate of Mark Roberts. Mark brings him up as a partner in a new business venture following his dismissal from the bank. His supposed involvement provides a sense of stability and forward momentum for Mark's career prospects in the wake of his job loss.

Michelle is the mother of Holli Byford. She encounters Erin when the filmmaker arrives at her home for a follow-up interview, only to reveal that Holli has recently gone missing, bringing unexpected police attention to their doorstep.