Bartimaeus The Amulet of Samarkand (Book One) - Jonathan Stroud

Nathaniel is a magician's apprentice, taking his first lessons in the arts of magic.
But when a devious hot-shot wizard named Simon Lovelace ruthlessly humiliates Nathaniel in front of his elders, Nathaniel decides to kick up his education a few notches and show Lovelace who's boss.
With revenge on his mind, he summons the powerful djinni, Bartimaeus.
But summoning Bartimaeus and controlling him are two different things entirely, and when Nathaniel sends the djinni out to steal Lovelace's greatest treasure, the Amulet of Samarkand, he finds himself caught up in a whirlwind of magical espionage, murder, and rebellion.