In the first pages of this novel we're introduced to an England of the early 19th Century, where though mostly the same as our own England, scholar magicians spend their evenings in the polite company of fellow gentlemen musing on the facts, though rarely the implications of the historical practice of magic on the isle. This status quo of scholarly men discussing scholarly things, but declining to actually experiment with their particular area of expertise is soon disturbed by a young upstart known as John Segundus. Segundus dares to ask a question to the effect of "Why don't English magicians actually practice magic anymore?" That question proves to be one of the strongest themes of the entire work as the reader is pushed, pulled, and contorted in many other ways as the two English individuals of the title take it upon themselves to revive the practice of magic.
Ms. Clarke introduces us to the period's first "practical magician," Mr. Gilbert Norrel through John Segundus' attempt to answer his own question. Norrel is depicted as snobbish, antisocial, reclusive, bookish, and of a refined, though arrogant demeanor. In short, he is the stereotypical English country gentleman. Clarke eventually takes Norrel and his truly insightful servant, Childermass, to London, where she lets us meet many of the luminaries of English politics and high society.
The characterization of every person is brilliantly detailed. There is not a servant, politician, soldier, magician, or vagabond that isn't treated as a full individual and graced with quirks and idiosyncrasies unique to them. A pleasant effect of this deliberate attention is that while getting into the story it's not easy to ascertain who is a major player, who is a supporting role, and who is just there to take up space. In fact, no character is there merely to take up space, and one character's social station has no effect on their influence in the story.
One would be remiss not to mention the undeniably English feel to the story, prose, and characters. This is a story about English characters in England. Even when the characters are most certainly not in England, they strive to transform their environment to one more like England. They seek out the company of other English people, they arrange their things to a more English sensibility, and in some cases the fact that the land around them isn't English leads the characters to regard that land as a minor annoyance as opposed to an actual place. However, being away from England has a special effect on those characters that alienates them from their contemporaries that have stayed on the island. They take pride in being English, but the condition of being so far from anything that they can identify as English warps what that means to them, and thus those characters who remain in England are eventually less likely to identify with the travelers as they're gone and after they return.
There are, of course, exceptions to all of this. There are major characters that are not English, but the condition of them being in England or interacting with the country and its people is a strong part of their character.
Just as much as England is a character, magic is a character in this story. For most of the story magic is not only a character metaphorically, but literally, in the form of the fairy gentleman with the thistle-down hair. His nature betrays the nature of magic and offers insight into the answer to John Segundus' question, "Why don't English magicians practice magic anymore?"
Finally, though the pacing could possibly be improved, the flaws therein are smoothed over by Clarke's satisfying resolution. Clarke brings the story to a fulfilling end, not tying up all of the loose ends, but finishing the story in a place well suited for such a purpose leaving the reader space to imagine.