Inspector Jackson is a detective working for Scotland Yard in the 19th-century London setting of the series. He serves as a primary adult authority figure in the law enforcement community, initially positioned as the professional investigator whom citizens would normally turn to for help with crimes and mysteries. As a representative of official police power, he is a corpulent and burly man with a somewhat imposing physical presence. His appearance includes gray hair and a mustache, and he is often seen wearing a hat and carrying a staff.

Jackson possesses a gruff and grumpy exterior, frequently expressing frustration through sighs and muttering. This temperament stems largely from his professional pride being challenged. His most defining personality trait is a deep-seated insecurity regarding his own investigative abilities. From the outset, Jackson is never fond of the young protagonist Angie, as he constantly feels threatened by the fact that the twelve-year-old girl is much sharper and more intelligent than he is. He perceives her natural talent for deduction as a direct threat that takes his spotlight away from him as the lead detective. This makes him initially resistant to her involvement in police matters, as he chafes at the intrusion of a noble adolescent girl into his domain. He must also endure the open admiration his own young assistant, Michael, shows for Angie's keen mind, which only adds to his exasperation.

Jackson's primary role in the story is as a collaborator and a contrast to the titular character, Angie Islington, who is an honorary detective rewarded by the Queen. He represents the established, traditional methods of policing, which are constantly shown to be less effective than Angie's brilliant intuition and clever plans. Despite his gruff resistance, he is a necessary part of the team, providing the official authority and adult presence that allows their adventures to proceed. His relationship with Angie is the central dynamic of his character. While he is often irritated by her involvement, he is repeatedly shown that without her significant contributions, the investigations would end with the arrest of the wrong suspect. This forces him into a position of reluctant respect, as he cannot deny the results she produces. He also works alongside his dashing assistant Michael, with whom he has a more traditional superior-subordinate relationship.

Over the course of the series, Inspector Jackson undergoes a subtle but clear development. He begins as an adult who doubts the capability of a child, but his thoughts of doubt gradually vanish as he is repeatedly confronted with evidence of Angie's talents. The pendant awarded to Angie by the Queen serves as an emblem of recognition that even someone in his position cannot easily dismiss. While his personality does not fundamentally change into a warm or effusive character, he evolves from being a reluctant and threatened authority figure into a grudgingly accepting ally. He is moved from a position of active resistance to one of resigned cooperation, where he has to admit that the young girl's assistance is not only helpful but often essential to bringing peace back to the town. As a detective, his notable ability lies in his official capacity and experience, but the narrative consistently highlights that his conventional skills are inferior to Angie's more creative and deductive reasoning.