Shadow in the North has a large cast of characters, some of whom play briefly prominent roles and then fade into the background. Theater stagehands, street urchins, and titled members of British society intermingle freely with the main characters, each adding some color to the story and filling in another piece of the puzzle. The main players in the story remain the focal point, however.

Most prominent in Shadow in the North is Sally Lockhart, a forthright young woman with a background in "firearms and finance," but not possessing the skills to "make small talk, dance gracefully, [and] flirt with a stranger at dinner while unerringly picking up the right knife and fork." Sally insists on being in the center of the action, but she would rather not rush into a situation blindly. Before confronting Axel Bellmann, she researches his firm and puts together her own conclusions from the information gathered. In many ways, Sally is a modern character, possessing a keen sense of right and wrong that does not fit with her society's views but strong enough to defend her beliefs and fight for them when necessary.

Frederick Garland alternately loves Sally and feels infuriated by her. Honest, moral, and resourceful, Fred is always ready to take on a challenge. While investigating Nellie Budd, he enters into an assumed role as a professor studying spiritualistic phenomena, but he just as easily becomes her friend and then her avenger when Bellmann's hired thugs attack her. While averse to violence—he tells Mackinnon at one point that he will investigate Bellmann, but won't be "body-guarding you . . . I've had my fill of brawling"—he will fight when necessary. Overall, Fred is a good and decent man, courageous and self-sacrificing to the end.

Perhaps the most interesting and realistic of the main characters is Jim Taylor, Sally and Fred's best friend. Coming from London's working classes, he can get access to some places and information that the others cannot. His network of acquaintances includes barmaids, stagehands, jockeys, pick pockets, and a myriad of others. Through this network, he locates Alistair Mackinnon in a seedy section of London and, in a humorous scene, verbally spars with the landlady's young daughter for the information he needs. Clever, intelligent, friendly, and protective, Jim is completely faithful to his friends. When he learns of Fred's death, he cries unabashedly, "Men didn't cry in the fiction Jim read and wrote, but they did in real life . . . Jim's father had cried when consumption had carried off his wife . . . when Jim was ten . . . There was no shame in it. There was honesty." Then knowing Sally will be hurting more, he seeks her out, despite his own emotional and physical pain.

Lady Mary Wytham and Isabel Meredith are two versions of the same person. Both love Mackinnon, protecting and hiding him from Bellmann, and both are connected with beauty in some way. Pullman describes Lady Mary as "a wild bird or young animal . . . all delicacy and shy fire" in her etherealness, while Isabel creates delicately beautiful garments with her needle. Neither enjoys "doing things," as Lady Mary tells Jim while they walk in the park. Isabel refuses to save herself or Fred from the house fire, preferring to let him die with her than to take any action with her own life. Lady Mary chooses a similar course of action in regards to her family. Although she knows that publicly acknowledging her marriage to Mackinnon would save him and her family from Bellmann's control, she finds it easier...