Bess is a 28-year-old content moderator for a dating app who lives a solitary life near the Salton Sea. Moving from England to Calabasas in her youth left her feeling alienated until she bonded with Joni and Evangeline. The tragic events of their 2008 high school graduation trip to Greece deeply traumatized her, prompting her to avoid public attention entirely. She drinks heavily and relies on a quiet routine to maintain her safety from the aggressive true crime media.

Joni is a highly successful wellness influencer with a massive online following and a glamorous lifestyle in Malibu. In her youth, she possessed a fierce temper and a brash personality that both intimidated and inspired Bess. She built her contemporary brand on the concept of radical honesty, using the media attention from her past to establish a lucrative career. Beneath her polished exterior, she exhibits an intense need for control and a willingness to manipulate others to protect her image.

Evangeline is a wealthy young woman whose 2008 death during a summer vacation in Mykonos initiates the central mystery. Before the tragedy, she acts as the stabilizing force in her friend group, offering a placid temperament that contrasts with Joni's intensity. As the daughter of an immensely wealthy family, she provides her friends with lavish opportunities but expects strict adherence to her preferences in return. Her sudden fall from a cliff ignites an international media frenzy.

Theo is Evangeline's brother, an attractive young man who arrives in Greece during a summer tour of Europe. He struggles with the emotional distance of his parents and occasionally feels smothered by Evangeline's intense reliance on him. His presence on the island shifts the social dynamics between the three young women. In 2018, he runs an investment company and continues trying to contact Bess.

Steven is Bess's protective older brother who worries constantly about her reclusive lifestyle. He harbors a long-standing distrust of Joni, viewing her as a ruthless individual who takes advantage of his sister. He remains fiercely defensive of Bess and spends his free time actively attempting to clear her name on internet true crime forums.

Willa is a prominent social media star and Joni's long-term partner in 2018. She maintains a highly curated public relationship with Joni that hides underlying personal tensions and betrayals. Her sudden disappearance forces Joni to seek out an alibi, drawing Bess back into the public eye.

Nova is Steven's fiancée who attended the University of Southern California in the same class as Willa. She shares Steven's wariness regarding Joni and is uncomfortable with the media circus that surrounds her.

Sophia is a sleek, beautiful fashion journalist who is married to Theo in the 2018 timeline.

Zoey is the woman Joni secretly sees outside of her relationship with Willa, acting as the initial catalyst for Joni's urgent need for a falsified alibi.

Ryan is a local cashier who recognizes Bess from the infamous true crime coverage of her youth. He acts kindly toward her, refusing to give reporters her address when they come looking for information.

Bardo is a friend of Theo who travels with him through Europe. Following the tragedy in Mykonos, he provides media interviews that publicly characterize the girls' friendship in a highly damaging light.