Lyra is an 18-year-old college student from London who urgently needs money to save her family home, Mile's End. She represses traumatic memories of witnessing her biological father's death, a burden that socially isolates her. A sharp observer with exceptional puzzle-solving skills, she processes the world through movement and touch. She traded her early background in dance for long-distance running to distance herself from her pain.

Rohan is a secretive young man raised by the leader of a powerful underground club. Tasked with earning 10 million pounds to secure his future position in the organization, he enters the game with cold determination. He operates as a chameleon, adopting whatever persona is most useful to gather information and win.

Gigi is an eccentric, highly optimistic 18-year-old with a habit of breaking into homes to leave gifts behind. Constantly battling feelings of inferiority compared to her sister, she uses her bubbly personality to mask her insecurities. She enters the competition wanting to give the prize money away to make amends for the crimes of her late father.

Savannah is a college basketball player and Gigi's fiercely competitive twin sister. Pale and athletically built, she handles the island's physical challenges with ease despite a recent surgery. She is highly intelligent, perceptively seeing through other players' tactics, and plays for deeply personal motivations concerning her family.

Grayson is the businesslike, silver-eyed second-oldest Hawthorne brother. Initially serving as the hosts' representative on the island to ensure the game runs smoothly, he finds himself drafted into the competition as the eighth player. He struggles with a need for control stemming from his rigorous upbringing under his grandfather.

Brady is a competitor in his early twenties who presents himself as friendly and protective. Having played the game previously, he arrives with knowledge of the structure and the other players. He actively courts Gigi's attention, positioning himself as a reliable ally while harboring his own intense desire to win on behalf of a sponsor.

Knox is an aggressive, surly competitor in his mid-twenties. Playing on behalf of wealthy sponsors, he prioritizes winning over making friends and frequently clashes with his former close friend, Brady. Under his rough exterior, he is fiercely loyal to the few people he considers family.

Odette is an 81-year-old woman with silver hair who participates in the game despite suffering from a terminal illness. She possesses a sharp, observant mind and a wealth of life experience from her past careers as an actress, housekeeper, and lawyer. She acts as a stabilizing presence on her team, offering wisdom rather than physical exertion.

Avery is the young billionaire who inherited the Hawthorne fortune and now co-hosts the Grandest Game. She designs the competition to offer others the life-changing opportunities she received, watching the participants carefully from behind the scenes.

Jameson is one of the Hawthorne brothers and a co-designer of the game. He thrives on puzzles and risk-taking, actively managing the game's mechanics and delivering key instructions to the players alongside Avery.

Nash is the eldest Hawthorne brother and one of the game's designers. He takes a laid-back but highly observant approach to the competition, keeping a close eye on dangerous players while maintaining a relaxed demeanor.

Xander is the youngest Hawthorne brother, known for his mechanical ingenuity. He helps coordinate the island's complex traps and puzzles, bringing an energetic enthusiasm to his role as a host.

Thomas is Lyra's biological father, a somewhat shady figure who told varying stories about his background. His death by suicide and his cryptic final words serve as the central mystery driving Lyra's investigation on the island.

Calla is a missing young woman from a wealthy family whose disappearance six years ago caused the severe falling out between Brady and Knox. Her absence deeply impacts both men's motivations in the current game.

The Proprietor is the aging head of the Devil's Mercy, a powerful underground club in London. He raised Rohan and sets the massive financial challenge that brings his protégé to the Grandest Game.