Cassidy is a 12-year-old girl with a round face, brown hair, and an antique camera worn constantly around her neck. Following a near-drowning incident the previous year, she gained the ability to cross into the Veil, a ghostly dimension overlapping the living world. She feels a profound sense of duty to find trapped spirits and help them move on. Her impulsive nature often pushes her into dangerous situations to protect innocent bystanders from paranormal harm.

Jacob is a 12-year-old ghost permanently dressed in worn jeans and a superhero T-shirt. Because he saved Cassidy from drowning, the two share a unique psychic bond that allows him to read her mind and exist in the physical world. He acts as a cautious, humorous foil to her recklessness. He constantly worries about her safety while hiding his own fears about his growing spectral strength.

Thomas is a dangerously powerful poltergeist presenting as a young boy in early 20th-century clothing. Separated from the memory of his own identity and death, he operates entirely on chaotic energy and anger. He views the physical world as a playground for violent mayhem, creating accidents that threaten Cassidy and the citizens of Paris.

Cassidy's parents operate as a charismatic pair of paranormal investigators, pairing his scholarly historical knowledge with her talent for storytelling. They travel the globe exploring famously haunted locations for their television show. Ironically, they remain completely unaware that their daughter possesses actual supernatural abilities, viewing their ghostly investigations through a purely theoretical lens.

Lara is a blunt, highly intelligent peer from Edinburgh who shares Cassidy's ability to cross into the spirit dimension. Operating with significantly more experience, she functions as a vital off-site advisor. She translates French clues, identifies the nature of the poltergeist, and coordinates the delivery of protective magical supplies to aid her friend.

Pauline is a polite Parisian local hired to escort the television production to famous historical sites like the Catacombs. She publicly identifies as a skeptic who rejects the existence of ghosts. Privately, she exhibits intense nervousness around haunted locations and relies on protective charms.

Adele is a young Parisian girl who holds crucial historical information about her family's past. Eager to involve herself in the supernatural investigation, she provides physical evidence and historical context regarding a local tragedy. Her enthusiasm for ghost stories drives her to offer translation assistance and local knowledge.

Sylvaine is a Parisian woman guarding the painful history of her grandfather's brother. She fiercely protects her family's privacy and refuses to discuss the events that occurred in the Catacombs, carrying the intergenerational grief resulting from a childhood accident.

Richard is a boy from the early 20th century who snuck into the underground tunnels to play hide-and-seek with his brother. He spent the rest of his life blaming himself for the tragic accident that occurred in the dark.

Anton is half of the sibling camera crew responsible for filming the reality television program. He follows the hosts through dark tunnels and historic opera houses to capture engaging content for viewers.

Annette is a member of the television production crew filming in France. She works alongside her brother to record the hosts as they narrate ghost stories in eerie underground locations.

Grim is the family's pet cat, brought along for their European travels. His presence serves as a convenient scapegoat when invisible supernatural forces cause destruction in their hotel room.