This note contains spoilers for the book.

Starts out to be a girl in a magic school. Although the magic school hardly teaches magic, and some of the students don't even believe in it. Note that this pre-dates J. K. Rowling, not that this is the only book about young wizards or a wizardry school to do so by a long shot.

However, the school turns out to be an early section, and the girl graduates and goes on to something very like a quest, by the end of which she is the Warden of the West, one of the four powers who ensure the balance of magic in the world. Along the way she defeats the sinister designs of her guardian, and finds her true love.

The world this is set in is ours, in 1908, pretty much; except for the existence of this magic and these schools. People are playing with early motor cars.