The Amulet of Samarkand is the first book in the Bartimaeus trilogy and a great origin story for Nathaniel, who becomes the Magician’s Apprentice John Mandrake.

The book does a great job of explaining the magic system in this alternate history of London.  We hear about past wars with Prague and great historic battles in Egypt and other locations.  These add a colorful background of world-building that helps to immerse you in the story.

In this world, when you show magical aptitude, you are removed from your family and taken on as an apprentice by a full-fledged magician.  The main source of magic is from summoning various forms of demons that range from weak sprites and imps to stronger foliots, djinni, then the powerful afrits and marids!  These summoned beings become slaves and perform magic duties for the wizards.  Some of their powers can be imbued into objects, while others are classic spells of power like a fireball.  

There is a constant battle using command words and rituals involving pentagrams that wages between the magicians and their summoned help.  When the demons win, the magicians usually die.  This story is about a child prodigy who could not stand the glacial pace of instruction from his master and summoned a djinni on his own, which set into motion world-changing effects (at least for Nathaniel).