We encountered Kitty, a member of what is effectively a terrorist cell, way back in Book One, The Amulet of Samarkand. It turns out that more and more commoner children like Kitty are being born with the ability to see through the hocus-pocus used to oppress them. Stroud's sympathies are definitely with the Muggles.
In Book Two, The Golem's Eye, we met the terrifying afrit (another type of demonic entity) Honorius, inhabiting the bones of the long-dead magician, Gladstone. The implications of this - demons incarnating in human bodies, albeit dead ones - are horrifyingly fleshed out in Ptolemy's Gate.
Kitty and her crew disturbed Gladstone's tomb in Westminster Abbey in order to retrieve the prime minister's staff of power (rather incompetently wielded by Nathaniel - no Harry Potter he). In this book, hell quite literally breaks loose, the uneasy balance between demons and men is destroyed, anarchy is loosed upon the world and the staff and the amulet return to play a part in the gloriously dark finale.
There are many delights to savour in this series. First and foremost, the wonderful, sardonic voice of the all-knowing and all-weary Bartimaeus, whose wit is often deployed in footnotes. Then there's Stroud's inventiveness as he rewrites world history (Bartimaeus helped build the walls of Prague, the Great Pyramid and most of the Seven Wonders; and the American War of Independence, taking place at the time of the series, is a rebellion against colonialist British magic). Finally, there's the robust way Stroud deals with Nathaniel. Unlike J K Rowling, always on hand to ensure that Harry grabs the snitch, finds the spell and trounces Slytherin, Stroud exhibits a profound scepticism towards his his boy protagonist. His sympathies lie rather with Bartimaeus, wrenched time and time again out of the Other Place into this world to do Nathaniel's bidding. Throughout The Golem's Eye, Nathaniel only intermittently displayed any good qualities. Ptolemy's Gate is his last chance to redeem himself.
But the signs aren't promising. Only 17, he's a member of the government, basking in acclaim and wealth, responsible for writing crude propaganda to fool the commoners into believing the American war can be won. His transformation into cold, unfeeling John Mandrake is almost complete.
Among all the horror and comedy, there's satire which verges on the uncomfortable. The magical government looks like New Labour, full of smiling, smarmy spin. Colleagues are backstabbers. An "enemy within" is bringing terror to London with a series of explosions. Only Bartimaeus, from the perspective of centuries of existence, comes up with the right response. He laughs.