The last officially recognized English wizard and a mentor to Peter, who embodies the tradition of magic in Britain. He guides Peter into the magical world, revealing the depth of his own history and knowledge.

A fellow probationary constable and professional rival to Peter, known for her competence and ambition in conventional police work. Her role becomes crucial as she investigates alongside Peter, navigating the intersection of police reality and magic.

The novel's antagonist, consisting of the ghost of an 18th-century actor and a chaotic entity from folklore. This dual character personifies unsuspected grievances and supernatural possession.

The head of the Westminster Murder Investigation Team, who is skeptical of supernatural explanations and adheres strictly to conventional policing methods. Represents the institutional challenge to integrating magical elements into police work.

The personification of the tidal portion of the River Thames, depicted as a powerful Nigerian matriarch. She rules over a court of river spirits and negotiates with the police as a formidable and influential presence.

The genius loci of the non-tidal part of the Thames, representing a traditional and rural England. He is involved in a territorial conflict with Mama Thames, reflecting deeper historical roots.

A spirit of a South London river and one of Mama Thames's daughters, who acts as a go-between for Peter. She embodies the fusion of ancient power and modern youth culture.

The enigmatic housekeeper of the Folly, dressed in an Edwardian maid’s uniform. Possessing non-human traits, she maintains the building and demonstrates loyalty and magical capabilities.

The ghost of a Victorian-era pickpocket haunting Covent Garden, who plays a key role in validating Peter’s supernatural experiences. His initial testimony is crucial in setting off the plot.

Also known as Lady Ty, a spirit of a lost London river and one of Mama Thames’s daughters. She has political ambitions and challenges Nightingale, aiming to modernize the handling of the supernatural.