In this book orphans or unwanted children are trained as apprentices to magicians and they learn magic like a trade. Magicians have no power in themselves but they derive it from learning how to control demons from the "other place." Nathaniel is a precocious apprentice to an ignorant master. After he is publicly humiliated by another magician, Simon Lovelace, he makes it his mission to avenge himself. He summons the demon Bartimaeus to steal a powerful amulet from Lovelace, unknowingly getting the two of them involved in a dark scheme.

There is no clear "good guy" in this book: Simon Lovelace is obviously slimy and bad, Nathaniel is pitiful and you want him to turn out good but he's also arrogant and ambitious, and Bartimaeus is, of course, a demon. Completely selfish, but he is also awesome. His chapters are incredibly interesting, funny, and amusing. He is the reason for the success of the story.

Nothing very deep going on here (at all), just a lot of fun.