Nick is a 25-year-old Oxford graduate who takes a job as an English schoolmaster on the remote Greek island of Phraxos to escape his mundane life in England. He struggles with commitment and often adopts a cynical, existentialist posture to hide his feelings of inadequacy. His desire for adventure and novelty draws him into a mysterious, highly psychological environment curated by a wealthy older man on the island.

Alison is a young Australian woman training to become an air hostess. She is emotionally frank, highly perceptive, and carries trauma from a previous relationship in Sydney. Her genuine affection and demand for emotional honesty stand in sharp contrast to Nick's cynical posturing, creating significant tension before he departs for his new job in Greece.

Conchis is a wealthy, deeply tanned, and enigmatic older man living on the Bourani headland of Phraxos. Rumored by locals to have a controversial past during World War II, he behaves like a theatrical director, creating elaborate masques and recounting complex stories about his life. He deliberately disorients his guests to challenge their perceptions of reality and free will.

Julie is a beautiful, pale-skinned British woman whom Nick encounters at Bourani. Initially introduced under the guise of Lily Montgomery, she presents herself as a young amateur actress entangled in Conchis's psychological experiments. Her presence deeply captivates Nick, pulling him further away from his ordinary life and into the mysteries of the island.

June is Julie's twin sister, characterized by a bolder and more direct demeanor than her sibling. Like Julie, she is an amateur actress from England who has found herself involved in the strange theatrical environment maintained by Conchis at Bourani.

Lily is an older, sophisticated woman who holds a strong connection to Maurice Conchis's past. She resides in London and possesses a deep understanding of the psychological exercises Conchis orchestrates, acting as a figure of authority and wisdom who provides guidance to those confused by the events at Bourani.

Mitford is Nick's immediate predecessor at the school on Phraxos. Presenting himself as a seasoned army veteran, he offers Nick practical advice about the island but provides a cryptic, dramatic warning to beware of the "waiting-room" at Bourani before departing.

Leverrier is an English teacher who worked at the Lord Byron school prior to Mitford. Nick discovers evidence that Leverrier frequently visited Bourani, contradicting local rumors about Conchis's isolation and sparking Nick's initial curiosity about the estate.

Demetriades, nicknamed "Meli," is the other English teacher at the school on Phraxos. He acts as Nick's primary source of local gossip, sharing the island's rumors about Conchis's alleged wartime collaboration.

Hermes is an older local man who previously worked as a handyman and donkeyman for Conchis. He provides Nick with an alternative account of Conchis's past during the German occupation, challenging the local rumors of collaboration.

Maria is a tiny older woman who works as the housekeeper at Conchis's villa. She maintains the domestic aspects of the household, wordlessly serving meals amidst the strange and theatrical events occurring around the property.

Margaret, known as Maggie, is Nick's Australian downstairs neighbor. She is friendly and welcoming, inadvertently facilitating Nick's introduction to Alison by inviting him to her gathering.

Pete is Margaret's brother and Alison's intermittent boyfriend. He works for an airline and is eager to marry Alison and settle down, though she remains hesitant about committing to him.

De Deukans is a wealthy, eccentric misogynist whom Conchis claims to have met during his youth. In Conchis's narrative, De Deukans is a collector of rare art and unusual mechanical devices who deeply influences a young Conchis's philosophical worldview with his hedonism.

Henrik is a visually impaired, fiercely religious Norwegian man who isolates himself in a freezing hut to wait for God. His intense spiritual ecstasy challenges Conchis's belief in pure scientific rationalism, demonstrating a different kind of authentic experience.

Anton is a music-loving young German officer who commands troops on Phraxos during World War II. He forms an unlikely bond with Conchis over art and culture, but struggles morally under the command of his ruthless superior officer.

Colonel Wimmel is a ruthless, sadistic senior German officer who oversees the military presence on Phraxos. He forces impossible and brutal choices upon the local villagers, acting as a physical manifestation of cruelty and absolute power in Conchis's historical account.

Joe is a tall Black man who participates in the elaborate theatricals at Bourani. He frequently acts as a watchful guardian or enforcer within Conchis's estate, physically intervening when the "rules" of the masque are broken or when Nick crosses a boundary.

Joan, who prefers to go by her surname Kemp, is Nick's bohemian landlady. She provides him with a warm, maternal presence and practical support when he returns to England in a distressed and vulnerable state.

Jojo is a 17-year-old, working-class art student from Glasgow. She develops a crush on Nick, who initially pays for her platonic companionship in an attempt to prove his own emotional fortitude and changed nature to whoever might be watching him.

Ann is Margaret's roommate in the flat below Nick's original London residence. She corresponds with Nick, relaying important information about Alison's wellbeing while he is isolated in Greece.

Mavromichalis is the deputy headmaster at the prep school on Phraxos. He manages the official affairs of the teachers and acts as an intermediary, occasionally delivering messages or reading materials to Nick that suggest a deeper connection to the island's mysteries.