Sophie is an outspoken 15-year-old girl whose parents are away on an archaeological dig. She considers herself the logical thinker of the family, relying on observation and deduction to make sense of the world. Her ordinary summer shatters when she witnesses a magical confrontation, pulling her into an ancient, hidden war. She is highly protective of her twin brother and attempts to rationalize the impossible events unfolding around them.

Josh is a 15-year-old boy working a summer bookstore job in San Francisco. He is physically large for his age and describes himself as impulsive and action-oriented. He heavily distrusts unscientific claims and struggles to accept the existence of magic. When supernatural violence erupts, his immediate instinct is to shield his sister and find practical solutions.

Nicholas Flamel is an immortal alchemyst born in 1330 who survives using an Elixir of Life brewed from an ancient book. He hides his extraordinary nature behind the facade of an ordinary, pale-eyed bookstore owner in San Francisco. He serves as a guide to the twins, utilizing his vast historical knowledge to keep them alive, though he guards his long-term plans with intense secrecy.

Perenelle is a centuries-old sorceress and the wife of Nicholas Flamel. She possesses immense magical power, including the rare ability to commune with the dead. Abducted early in the conflict, she is forced to rely on her cunning and distant magical interventions to assist her husband and the teenagers from afar.

Dr. John Dee is an immortal magician who once apprenticed under Nicholas Flamel before swearing allegiance to the Dark Elders. He presents himself as an impeccably dressed man in a tailored charcoal suit with a neat triangular beard. He pursues an ancient text to reshape the world on behalf of his masters, employing dark magic, necromancy, and monstrous creatures to track his targets.

Scathach is a 2,000-year-old warrior of the Next Generation Elder race. She appears as a red-haired teenage girl with pale skin and green eyes, speaking with a distinct Irish accent. Having trained many historical heroes in combat, she agrees to protect the twins and uses her extensive martial knowledge to fend off magical threats.

Hekate is the Goddess with Three Faces, an ancient Elder who rules a localized, magical domain built around a massive World Tree. Her physical form changes depending on the time of day, aging from a young girl in the morning to an old woman at night. She possesses the unique ability to awaken dormant magical potential in humans.

The Morrigan is a Dark Elder known as the Goddess of Death and Destruction. She acts as a terrifying enforcer for Dr. John Dee's cause. She controls massive flocks of crows, which she uses as spies, trackers, and aerial weapons to hunt Flamel and the twins across California.

Bastet is an ancient Egyptian Elder who appears as a woman with a cat's head. She commands the absolute loyalty of felines and can transform them into dangerous half-human warriors. She is recruited by the Morrigan to assist in a massive assault on a rival Elder's territory.

The Witch of Endor, who goes by Dora, is an ancient being possessing the power of Sight. She traded her physical vision to see patterns of time, leaving her blind but capable of viewing the world through reflective surfaces. She uses her mastery of Air magic to assist those fighting against the Dark Elders.

Elle is Sophie's teenage friend in San Francisco. She represents the normal, mundane life that Sophie is abruptly forced to leave behind once the magical conflict begins.

Agnes is the aunt of Sophie and Josh Newman. She hosts them in San Francisco during the summer while their parents work on an archaeological dig.